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Research Methods – Types, Examples and Guide

Table of Contents

Research Methods

Definition:

Research Methods refer to the techniques, procedures, and processes used by researchers to collect , analyze, and interpret data in order to answer research questions or test hypotheses. The methods used in research can vary depending on the research questions, the type of data that is being collected, and the research design.

Types of Research Methods

Types of Research Methods are as follows:

Qualitative research Method

Qualitative research methods are used to collect and analyze non-numerical data. This type of research is useful when the objective is to explore the meaning of phenomena, understand the experiences of individuals, or gain insights into complex social processes. Qualitative research methods include interviews, focus groups, ethnography, and content analysis.

Quantitative Research Method

Quantitative research methods are used to collect and analyze numerical data. This type of research is useful when the objective is to test a hypothesis, determine cause-and-effect relationships, and measure the prevalence of certain phenomena. Quantitative research methods include surveys, experiments, and secondary data analysis.

Mixed Method Research

Mixed Method Research refers to the combination of both qualitative and quantitative research methods in a single study. This approach aims to overcome the limitations of each individual method and to provide a more comprehensive understanding of the research topic. This approach allows researchers to gather both quantitative data, which is often used to test hypotheses and make generalizations about a population, and qualitative data, which provides a more in-depth understanding of the experiences and perspectives of individuals.

Key Differences Between Research Methods

The following Table shows the key differences between Quantitative, Qualitative and Mixed Research Methods

Examples of Research Methods

Examples of Research Methods are as follows:

Qualitative Research Example:

A researcher wants to study the experience of cancer patients during their treatment. They conduct in-depth interviews with patients to gather data on their emotional state, coping mechanisms, and support systems.

Quantitative Research Example:

A company wants to determine the effectiveness of a new advertisement campaign. They survey a large group of people, asking them to rate their awareness of the product and their likelihood of purchasing it.

Mixed Research Example:

A university wants to evaluate the effectiveness of a new teaching method in improving student performance. They collect both quantitative data (such as test scores) and qualitative data (such as feedback from students and teachers) to get a complete picture of the impact of the new method.

Applications of Research Methods

Research methods are used in various fields to investigate, analyze, and answer research questions. Here are some examples of how research methods are applied in different fields:

• Psychology : Research methods are widely used in psychology to study human behavior, emotions, and mental processes. For example, researchers may use experiments, surveys, and observational studies to understand how people behave in different situations, how they respond to different stimuli, and how their brains process information.
• Sociology : Sociologists use research methods to study social phenomena, such as social inequality, social change, and social relationships. Researchers may use surveys, interviews, and observational studies to collect data on social attitudes, beliefs, and behaviors.
• Medicine : Research methods are essential in medical research to study diseases, test new treatments, and evaluate their effectiveness. Researchers may use clinical trials, case studies, and laboratory experiments to collect data on the efficacy and safety of different medical treatments.
• Education : Research methods are used in education to understand how students learn, how teachers teach, and how educational policies affect student outcomes. Researchers may use surveys, experiments, and observational studies to collect data on student performance, teacher effectiveness, and educational programs.
• Business : Research methods are used in business to understand consumer behavior, market trends, and business strategies. Researchers may use surveys, focus groups, and observational studies to collect data on consumer preferences, market trends, and industry competition.
• Environmental science : Research methods are used in environmental science to study the natural world and its ecosystems. Researchers may use field studies, laboratory experiments, and observational studies to collect data on environmental factors, such as air and water quality, and the impact of human activities on the environment.
• Political science : Research methods are used in political science to study political systems, institutions, and behavior. Researchers may use surveys, experiments, and observational studies to collect data on political attitudes, voting behavior, and the impact of policies on society.

Purpose of Research Methods

Research methods serve several purposes, including:

• Identify research problems: Research methods are used to identify research problems or questions that need to be addressed through empirical investigation.
• Develop hypotheses: Research methods help researchers develop hypotheses, which are tentative explanations for the observed phenomenon or relationship.
• Collect data: Research methods enable researchers to collect data in a systematic and objective way, which is necessary to test hypotheses and draw meaningful conclusions.
• Analyze data: Research methods provide tools and techniques for analyzing data, such as statistical analysis, content analysis, and discourse analysis.
• Test hypotheses: Research methods allow researchers to test hypotheses by examining the relationships between variables in a systematic and controlled manner.
• Draw conclusions : Research methods facilitate the drawing of conclusions based on empirical evidence and help researchers make generalizations about a population based on their sample data.
• Enhance understanding: Research methods contribute to the development of knowledge and enhance our understanding of various phenomena and relationships, which can inform policy, practice, and theory.

When to Use Research Methods

Research methods are used when you need to gather information or data to answer a question or to gain insights into a particular phenomenon.

Here are some situations when research methods may be appropriate:

• To investigate a problem : Research methods can be used to investigate a problem or a research question in a particular field. This can help in identifying the root cause of the problem and developing solutions.
• To gather data: Research methods can be used to collect data on a particular subject. This can be done through surveys, interviews, observations, experiments, and more.
• To evaluate programs : Research methods can be used to evaluate the effectiveness of a program, intervention, or policy. This can help in determining whether the program is meeting its goals and objectives.
• To explore new areas : Research methods can be used to explore new areas of inquiry or to test new hypotheses. This can help in advancing knowledge in a particular field.
• To make informed decisions : Research methods can be used to gather information and data to support informed decision-making. This can be useful in various fields such as healthcare, business, and education.

Advantages of Research Methods

Research methods provide several advantages, including:

• Objectivity : Research methods enable researchers to gather data in a systematic and objective manner, minimizing personal biases and subjectivity. This leads to more reliable and valid results.
• Replicability : A key advantage of research methods is that they allow for replication of studies by other researchers. This helps to confirm the validity of the findings and ensures that the results are not specific to the particular research team.
• Generalizability : Research methods enable researchers to gather data from a representative sample of the population, allowing for generalizability of the findings to a larger population. This increases the external validity of the research.
• Precision : Research methods enable researchers to gather data using standardized procedures, ensuring that the data is accurate and precise. This allows researchers to make accurate predictions and draw meaningful conclusions.
• Efficiency : Research methods enable researchers to gather data efficiently, saving time and resources. This is especially important when studying large populations or complex phenomena.
• Innovation : Research methods enable researchers to develop new techniques and tools for data collection and analysis, leading to innovation and advancement in the field.

About the author

Muhammad Hassan

Researcher, Academic Writer, Web developer

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What Is Research Methodology? A Plain-Language Explanation & Definition (With Examples)

By Derek Jansen (MBA)  and Kerryn Warren (PhD) | June 2020 (Last updated April 2023)

If you’re new to formal academic research, it’s quite likely that you’re feeling a little overwhelmed by all the technical lingo that gets thrown around. And who could blame you – “research methodology”, “research methods”, “sampling strategies”… it all seems never-ending!

In this post, we’ll demystify the landscape with plain-language explanations and loads of examples (including easy-to-follow videos), so that you can approach your dissertation, thesis or research project with confidence. Let’s get started.

Research Methodology 101

• What exactly research methodology means
• What qualitative , quantitative and mixed methods are
• What sampling strategy is
• What data collection methods are
• What data analysis methods are
• How to choose your research methodology
• Example of a research methodology

What is research methodology?

Research methodology simply refers to the practical “how” of a research study. More specifically, it’s about how  a researcher  systematically designs a study  to ensure valid and reliable results that address the research aims, objectives and research questions . Specifically, how the researcher went about deciding:

• What type of data to collect (e.g., qualitative or quantitative data )
• Who  to collect it from (i.e., the sampling strategy )
• How to  collect  it (i.e., the data collection method )
• How to  analyse  it (i.e., the data analysis methods )

Within any formal piece of academic research (be it a dissertation, thesis or journal article), you’ll find a research methodology chapter or section which covers the aspects mentioned above. Importantly, a good methodology chapter explains not just   what methodological choices were made, but also explains  why they were made. In other words, the methodology chapter should justify  the design choices, by showing that the chosen methods and techniques are the best fit for the research aims, objectives and research questions. 

So, it’s the same as research design?

Not quite. As we mentioned, research methodology refers to the collection of practical decisions regarding what data you’ll collect, from who, how you’ll collect it and how you’ll analyse it. Research design, on the other hand, is more about the overall strategy you’ll adopt in your study. For example, whether you’ll use an experimental design in which you manipulate one variable while controlling others. You can learn more about research design and the various design types here .

Need a helping hand?

What are qualitative, quantitative and mixed-methods?

Qualitative, quantitative and mixed-methods are different types of methodological approaches, distinguished by their focus on words , numbers or both . This is a bit of an oversimplification, but its a good starting point for understanding.

Let’s take a closer look.

Qualitative research refers to research which focuses on collecting and analysing words (written or spoken) and textual or visual data, whereas quantitative research focuses on measurement and testing using numerical data . Qualitative analysis can also focus on other “softer” data points, such as body language or visual elements.

It’s quite common for a qualitative methodology to be used when the research aims and research questions are exploratory  in nature. For example, a qualitative methodology might be used to understand peoples’ perceptions about an event that took place, or a political candidate running for president. 

Contrasted to this, a quantitative methodology is typically used when the research aims and research questions are confirmatory  in nature. For example, a quantitative methodology might be used to measure the relationship between two variables (e.g. personality type and likelihood to commit a crime) or to test a set of hypotheses .

As you’ve probably guessed, the mixed-method methodology attempts to combine the best of both qualitative and quantitative methodologies to integrate perspectives and create a rich picture. If you’d like to learn more about these three methodological approaches, be sure to watch our explainer video below.

What is sampling strategy?

Simply put, sampling is about deciding who (or where) you’re going to collect your data from . Why does this matter? Well, generally it’s not possible to collect data from every single person in your group of interest (this is called the “population”), so you’ll need to engage a smaller portion of that group that’s accessible and manageable (this is called the “sample”).

How you go about selecting the sample (i.e., your sampling strategy) will have a major impact on your study.  There are many different sampling methods  you can choose from, but the two overarching categories are probability   sampling and  non-probability   sampling .

Probability sampling  involves using a completely random sample from the group of people you’re interested in. This is comparable to throwing the names all potential participants into a hat, shaking it up, and picking out the “winners”. By using a completely random sample, you’ll minimise the risk of selection bias and the results of your study will be more generalisable  to the entire population. 

Non-probability sampling , on the other hand,  doesn’t use a random sample . For example, it might involve using a convenience sample, which means you’d only interview or survey people that you have access to (perhaps your friends, family or work colleagues), rather than a truly random sample. With non-probability sampling, the results are typically not generalisable .

To learn more about sampling methods, be sure to check out the video below.

What are data collection methods?

As the name suggests, data collection methods simply refers to the way in which you go about collecting the data for your study. Some of the most common data collection methods include:

• Interviews (which can be unstructured, semi-structured or structured)
• Focus groups and group interviews
• Surveys (online or physical surveys)
• Observations (watching and recording activities)
• Biophysical measurements (e.g., blood pressure, heart rate, etc.)
• Documents and records (e.g., financial reports, court records, etc.)

The choice of which data collection method to use depends on your overall research aims and research questions , as well as practicalities and resource constraints. For example, if your research is exploratory in nature, qualitative methods such as interviews and focus groups would likely be a good fit. Conversely, if your research aims to measure specific variables or test hypotheses, large-scale surveys that produce large volumes of numerical data would likely be a better fit.

What are data analysis methods?

Data analysis methods refer to the methods and techniques that you’ll use to make sense of your data. These can be grouped according to whether the research is qualitative  (words-based) or quantitative (numbers-based).

Popular data analysis methods in qualitative research include:

• Qualitative content analysis
• Thematic analysis
• Discourse analysis
• Narrative analysis
• Interpretative phenomenological analysis (IPA)
• Visual analysis (of photographs, videos, art, etc.)

Qualitative data analysis all begins with data coding , after which an analysis method is applied. In some cases, more than one analysis method is used, depending on the research aims and research questions . In the video below, we explore some  common qualitative analysis methods, along with practical examples.  

Moving on to the quantitative side of things, popular data analysis methods in this type of research include:

• Descriptive statistics (e.g. means, medians, modes )
• Inferential statistics (e.g. correlation, regression, structural equation modelling)

Again, the choice of which data collection method to use depends on your overall research aims and objectives , as well as practicalities and resource constraints. In the video below, we explain some core concepts central to quantitative analysis.

How do I choose a research methodology?

As you’ve probably picked up by now, your research aims and objectives have a major influence on the research methodology . So, the starting point for developing your research methodology is to take a step back and look at the big picture of your research, before you make methodology decisions. The first question you need to ask yourself is whether your research is exploratory or confirmatory in nature.

If your research aims and objectives are primarily exploratory in nature, your research will likely be qualitative and therefore you might consider qualitative data collection methods (e.g. interviews) and analysis methods (e.g. qualitative content analysis). 

Conversely, if your research aims and objective are looking to measure or test something (i.e. they’re confirmatory), then your research will quite likely be quantitative in nature, and you might consider quantitative data collection methods (e.g. surveys) and analyses (e.g. statistical analysis).

Designing your research and working out your methodology is a large topic, which we cover extensively on the blog . For now, however, the key takeaway is that you should always start with your research aims, objectives and research questions (the golden thread). Every methodological choice you make needs align with those three components. 

Example of a research methodology chapter

In the video below, we provide a detailed walkthrough of a research methodology from an actual dissertation, as well as an overview of our free methodology template .

Psst... there’s more!

This post was based on one of our popular Research Bootcamps . If you're working on a research project, you'll definitely want to check this out ...

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Thanks for your comment.

We can’t write your methodology for you. If you’re looking for samples, you should be able to find some sample methodologies on Google. Alternatively, you can download some previous dissertations from a dissertation directory and have a look at the methodology chapters therein.

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MLA Jansen, Derek, and Kerryn Warren. “What (Exactly) Is Research Methodology?” Grad Coach, June 2021, gradcoach.com/what-is-research-methodology/.

APA Jansen, D., & Warren, K. (2021, June). What (Exactly) Is Research Methodology? Grad Coach. https://gradcoach.com/what-is-research-methodology/

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• What Is a Research Methodology? | Steps & Tips

What Is a Research Methodology? | Steps & Tips

Published on 25 February 2019 by Shona McCombes . Revised on 10 October 2022.

Your research methodology discusses and explains the data collection and analysis methods you used in your research. A key part of your thesis, dissertation, or research paper, the methodology chapter explains what you did and how you did it, allowing readers to evaluate the reliability and validity of your research.

It should include:

• The type of research you conducted
• How you collected and analysed your data
• Any tools or materials you used in the research
• Why you chose these methods
• Your methodology section should generally be written in the past tense .
• Academic style guides in your field may provide detailed guidelines on what to include for different types of studies.
• Your citation style might provide guidelines for your methodology section (e.g., an APA Style methods section ).

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Table of contents

How to write a research methodology, why is a methods section important, step 1: explain your methodological approach, step 2: describe your data collection methods, step 3: describe your analysis method, step 4: evaluate and justify the methodological choices you made, tips for writing a strong methodology chapter, frequently asked questions about methodology.

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Your methods section is your opportunity to share how you conducted your research and why you chose the methods you chose. It’s also the place to show that your research was rigorously conducted and can be replicated .

It gives your research legitimacy and situates it within your field, and also gives your readers a place to refer to if they have any questions or critiques in other sections.

You can start by introducing your overall approach to your research. You have two options here.

Option 1: Start with your “what”

What research problem or question did you investigate?

• Aim to describe the characteristics of something?
• Explore an under-researched topic?
• Establish a causal relationship?

And what type of data did you need to achieve this aim?

• Quantitative data , qualitative data , or a mix of both?
• Primary data collected yourself, or secondary data collected by someone else?
• Experimental data gathered by controlling and manipulating variables, or descriptive data gathered via observations?

Option 2: Start with your “why”

Depending on your discipline, you can also start with a discussion of the rationale and assumptions underpinning your methodology. In other words, why did you choose these methods for your study?

• Why is this the best way to answer your research question?
• Is this a standard methodology in your field, or does it require justification?
• Were there any ethical considerations involved in your choices?
• What are the criteria for validity and reliability in this type of research ?

Once you have introduced your reader to your methodological approach, you should share full details about your data collection methods .

Quantitative methods

In order to be considered generalisable, you should describe quantitative research methods in enough detail for another researcher to replicate your study.

Here, explain how you operationalised your concepts and measured your variables. Discuss your sampling method or inclusion/exclusion criteria, as well as any tools, procedures, and materials you used to gather your data.

Surveys Describe where, when, and how the survey was conducted.

• How did you design the questionnaire?
• What form did your questions take (e.g., multiple choice, Likert scale )?
• Were your surveys conducted in-person or virtually?
• What sampling method did you use to select participants?
• What was your sample size and response rate?

Experiments Share full details of the tools, techniques, and procedures you used to conduct your experiment.

• How did you design the experiment ?
• How did you recruit participants?
• How did you manipulate and measure the variables ?
• What tools did you use?

Existing data Explain how you gathered and selected the material (such as datasets or archival data) that you used in your analysis.

• Where did you source the material?
• How was the data originally produced?
• What criteria did you use to select material (e.g., date range)?

The survey consisted of 5 multiple-choice questions and 10 questions measured on a 7-point Likert scale.

The goal was to collect survey responses from 350 customers visiting the fitness apparel company’s brick-and-mortar location in Boston on 4–8 July 2022, between 11:00 and 15:00.

Here, a customer was defined as a person who had purchased a product from the company on the day they took the survey. Participants were given 5 minutes to fill in the survey anonymously. In total, 408 customers responded, but not all surveys were fully completed. Due to this, 371 survey results were included in the analysis.

Qualitative methods

In qualitative research , methods are often more flexible and subjective. For this reason, it’s crucial to robustly explain the methodology choices you made.

Be sure to discuss the criteria you used to select your data, the context in which your research was conducted, and the role you played in collecting your data (e.g., were you an active participant, or a passive observer?)

Interviews or focus groups Describe where, when, and how the interviews were conducted.

• How did you find and select participants?
• How many participants took part?
• What form did the interviews take ( structured , semi-structured , or unstructured )?
• How long were the interviews?
• How were they recorded?

Participant observation Describe where, when, and how you conducted the observation or ethnography .

• What group or community did you observe? How long did you spend there?
• How did you gain access to this group? What role did you play in the community?
• How long did you spend conducting the research? Where was it located?
• How did you record your data (e.g., audiovisual recordings, note-taking)?

Existing data Explain how you selected case study materials for your analysis.

• What type of materials did you analyse?
• How did you select them?

In order to gain better insight into possibilities for future improvement of the fitness shop’s product range, semi-structured interviews were conducted with 8 returning customers.

Here, a returning customer was defined as someone who usually bought products at least twice a week from the store.

Surveys were used to select participants. Interviews were conducted in a small office next to the cash register and lasted approximately 20 minutes each. Answers were recorded by note-taking, and seven interviews were also filmed with consent. One interviewee preferred not to be filmed.

Mixed methods

Mixed methods research combines quantitative and qualitative approaches. If a standalone quantitative or qualitative study is insufficient to answer your research question, mixed methods may be a good fit for you.

Mixed methods are less common than standalone analyses, largely because they require a great deal of effort to pull off successfully. If you choose to pursue mixed methods, it’s especially important to robustly justify your methods here.

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Next, you should indicate how you processed and analysed your data. Avoid going into too much detail: you should not start introducing or discussing any of your results at this stage.

In quantitative research , your analysis will be based on numbers. In your methods section, you can include:

• How you prepared the data before analysing it (e.g., checking for missing data , removing outliers , transforming variables)
• Which software you used (e.g., SPSS, Stata or R)
• Which statistical tests you used (e.g., two-tailed t test , simple linear regression )

In qualitative research, your analysis will be based on language, images, and observations (often involving some form of textual analysis ).

Specific methods might include:

• Content analysis : Categorising and discussing the meaning of words, phrases and sentences
• Thematic analysis : Coding and closely examining the data to identify broad themes and patterns
• Discourse analysis : Studying communication and meaning in relation to their social context

Mixed methods combine the above two research methods, integrating both qualitative and quantitative approaches into one coherent analytical process.

Above all, your methodology section should clearly make the case for why you chose the methods you did. This is especially true if you did not take the most standard approach to your topic. In this case, discuss why other methods were not suitable for your objectives, and show how this approach contributes new knowledge or understanding.

In any case, it should be overwhelmingly clear to your reader that you set yourself up for success in terms of your methodology’s design. Show how your methods should lead to results that are valid and reliable, while leaving the analysis of the meaning, importance, and relevance of your results for your discussion section .

• Quantitative: Lab-based experiments cannot always accurately simulate real-life situations and behaviours, but they are effective for testing causal relationships between variables .
• Qualitative: Unstructured interviews usually produce results that cannot be generalised beyond the sample group , but they provide a more in-depth understanding of participants’ perceptions, motivations, and emotions.
• Mixed methods: Despite issues systematically comparing differing types of data, a solely quantitative study would not sufficiently incorporate the lived experience of each participant, while a solely qualitative study would be insufficiently generalisable.

Remember that your aim is not just to describe your methods, but to show how and why you applied them. Again, it’s critical to demonstrate that your research was rigorously conducted and can be replicated.

1. Focus on your objectives and research questions

The methodology section should clearly show why your methods suit your objectives  and convince the reader that you chose the best possible approach to answering your problem statement and research questions .

2. Cite relevant sources

Your methodology can be strengthened by referencing existing research in your field. This can help you to:

• Show that you followed established practice for your type of research
• Discuss how you decided on your approach by evaluating existing research
• Present a novel methodological approach to address a gap in the literature

3. Write for your audience

Consider how much information you need to give, and avoid getting too lengthy. If you are using methods that are standard for your discipline, you probably don’t need to give a lot of background or justification.

Regardless, your methodology should be a clear, well-structured text that makes an argument for your approach, not just a list of technical details and procedures.

Methodology refers to the overarching strategy and rationale of your research. Developing your methodology involves studying the research methods used in your field and the theories or principles that underpin them, in order to choose the approach that best matches your objectives.

Methods are the specific tools and procedures you use to collect and analyse data (e.g. interviews, experiments , surveys , statistical tests ).

In a dissertation or scientific paper, the methodology chapter or methods section comes after the introduction and before the results , discussion and conclusion .

Depending on the length and type of document, you might also include a literature review or theoretical framework before the methodology.

Quantitative research deals with numbers and statistics, while qualitative research deals with words and meanings.

Quantitative methods allow you to test a hypothesis by systematically collecting and analysing data, while qualitative methods allow you to explore ideas and experiences in depth.

A sample is a subset of individuals from a larger population. Sampling means selecting the group that you will actually collect data from in your research.

For example, if you are researching the opinions of students in your university, you could survey a sample of 100 students.

Statistical sampling allows you to test a hypothesis about the characteristics of a population. There are various sampling methods you can use to ensure that your sample is representative of the population as a whole.

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What is Research Methodology? Definition, Types, and Examples

Research methodology 1,2 is a structured and scientific approach used to collect, analyze, and interpret quantitative or qualitative data to answer research questions or test hypotheses. A research methodology is like a plan for carrying out research and helps keep researchers on track by limiting the scope of the research. Several aspects must be considered before selecting an appropriate research methodology, such as research limitations and ethical concerns that may affect your research.

The research methodology section in a scientific paper describes the different methodological choices made, such as the data collection and analysis methods, and why these choices were selected. The reasons should explain why the methods chosen are the most appropriate to answer the research question. A good research methodology also helps ensure the reliability and validity of the research findings. There are three types of research methodology—quantitative, qualitative, and mixed-method, which can be chosen based on the research objectives.

What is research methodology ?

A research methodology describes the techniques and procedures used to identify and analyze information regarding a specific research topic. It is a process by which researchers design their study so that they can achieve their objectives using the selected research instruments. It includes all the important aspects of research, including research design, data collection methods, data analysis methods, and the overall framework within which the research is conducted. While these points can help you understand what is research methodology, you also need to know why it is important to pick the right methodology.

Why is research methodology important?

Having a good research methodology in place has the following advantages: 3

• Helps other researchers who may want to replicate your research; the explanations will be of benefit to them.
• You can easily answer any questions about your research if they arise at a later stage.
• A research methodology provides a framework and guidelines for researchers to clearly define research questions, hypotheses, and objectives.
• It helps researchers identify the most appropriate research design, sampling technique, and data collection and analysis methods.
• A sound research methodology helps researchers ensure that their findings are valid and reliable and free from biases and errors.
• It also helps ensure that ethical guidelines are followed while conducting research.
• A good research methodology helps researchers in planning their research efficiently, by ensuring optimum usage of their time and resources.

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Types of research methodology.

There are three types of research methodology based on the type of research and the data required. 1

• Quantitative research methodology focuses on measuring and testing numerical data. This approach is good for reaching a large number of people in a short amount of time. This type of research helps in testing the causal relationships between variables, making predictions, and generalizing results to wider populations.
• Qualitative research methodology examines the opinions, behaviors, and experiences of people. It collects and analyzes words and textual data. This research methodology requires fewer participants but is still more time consuming because the time spent per participant is quite large. This method is used in exploratory research where the research problem being investigated is not clearly defined.
• Mixed-method research methodology uses the characteristics of both quantitative and qualitative research methodologies in the same study. This method allows researchers to validate their findings, verify if the results observed using both methods are complementary, and explain any unexpected results obtained from one method by using the other method.

What are the types of sampling designs in research methodology?

Sampling 4 is an important part of a research methodology and involves selecting a representative sample of the population to conduct the study, making statistical inferences about them, and estimating the characteristics of the whole population based on these inferences. There are two types of sampling designs in research methodology—probability and nonprobability.

• Probability sampling

In this type of sampling design, a sample is chosen from a larger population using some form of random selection, that is, every member of the population has an equal chance of being selected. The different types of probability sampling are:

• Systematic —sample members are chosen at regular intervals. It requires selecting a starting point for the sample and sample size determination that can be repeated at regular intervals. This type of sampling method has a predefined range; hence, it is the least time consuming.
• Stratified —researchers divide the population into smaller groups that don’t overlap but represent the entire population. While sampling, these groups can be organized, and then a sample can be drawn from each group separately.
• Cluster —the population is divided into clusters based on demographic parameters like age, sex, location, etc.
• Convenience —selects participants who are most easily accessible to researchers due to geographical proximity, availability at a particular time, etc.
• Purposive —participants are selected at the researcher’s discretion. Researchers consider the purpose of the study and the understanding of the target audience.
• Snowball —already selected participants use their social networks to refer the researcher to other potential participants.
• Quota —while designing the study, the researchers decide how many people with which characteristics to include as participants. The characteristics help in choosing people most likely to provide insights into the subject.

What are data collection methods?

During research, data are collected using various methods depending on the research methodology being followed and the research methods being undertaken. Both qualitative and quantitative research have different data collection methods, as listed below.

Qualitative research 5

• One-on-one interviews: Helps the interviewers understand a respondent’s subjective opinion and experience pertaining to a specific topic or event
• Document study/literature review/record keeping: Researchers’ review of already existing written materials such as archives, annual reports, research articles, guidelines, policy documents, etc.
• Focus groups: Constructive discussions that usually include a small sample of about 6-10 people and a moderator, to understand the participants’ opinion on a given topic.
• Qualitative observation : Researchers collect data using their five senses (sight, smell, touch, taste, and hearing).

Quantitative research 6

• Sampling: The most common type is probability sampling.
• Interviews: Commonly telephonic or done in-person.
• Observations: Structured observations are most commonly used in quantitative research. In this method, researchers make observations about specific behaviors of individuals in a structured setting.
• Document review: Reviewing existing research or documents to collect evidence for supporting the research.
• Surveys and questionnaires. Surveys can be administered both online and offline depending on the requirement and sample size.

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What are data analysis methods.

The data collected using the various methods for qualitative and quantitative research need to be analyzed to generate meaningful conclusions. These data analysis methods 7 also differ between quantitative and qualitative research.

Quantitative research involves a deductive method for data analysis where hypotheses are developed at the beginning of the research and precise measurement is required. The methods include statistical analysis applications to analyze numerical data and are grouped into two categories—descriptive and inferential.

Descriptive analysis is used to describe the basic features of different types of data to present it in a way that ensures the patterns become meaningful. The different types of descriptive analysis methods are:

• Measures of frequency (count, percent, frequency)
• Measures of central tendency (mean, median, mode)
• Measures of dispersion or variation (range, variance, standard deviation)
• Measure of position (percentile ranks, quartile ranks)

Inferential analysis is used to make predictions about a larger population based on the analysis of the data collected from a smaller population. This analysis is used to study the relationships between different variables. Some commonly used inferential data analysis methods are:

• Correlation: To understand the relationship between two or more variables.
• Cross-tabulation: Analyze the relationship between multiple variables.
• Regression analysis: Study the impact of independent variables on the dependent variable.
• Frequency tables: To understand the frequency of data.
• Analysis of variance: To test the degree to which two or more variables differ in an experiment.

Qualitative research involves an inductive method for data analysis where hypotheses are developed after data collection. The methods include:

• Content analysis: For analyzing documented information from text and images by determining the presence of certain words or concepts in texts.
• Narrative analysis: For analyzing content obtained from sources such as interviews, field observations, and surveys. The stories and opinions shared by people are used to answer research questions.
• Discourse analysis: For analyzing interactions with people considering the social context, that is, the lifestyle and environment, under which the interaction occurs.
• Grounded theory: Involves hypothesis creation by data collection and analysis to explain why a phenomenon occurred.
• Thematic analysis: To identify important themes or patterns in data and use these to address an issue.

How to choose a research methodology?

Here are some important factors to consider when choosing a research methodology: 8

• Research objectives, aims, and questions —these would help structure the research design.
• Review existing literature to identify any gaps in knowledge.
• Check the statistical requirements —if data-driven or statistical results are needed then quantitative research is the best. If the research questions can be answered based on people’s opinions and perceptions, then qualitative research is most suitable.
• Sample size —sample size can often determine the feasibility of a research methodology. For a large sample, less effort- and time-intensive methods are appropriate.
• Constraints —constraints of time, geography, and resources can help define the appropriate methodology.

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How to write a research methodology .

A research methodology should include the following components: 3,9

• Research design —should be selected based on the research question and the data required. Common research designs include experimental, quasi-experimental, correlational, descriptive, and exploratory.
• Research method —this can be quantitative, qualitative, or mixed-method.
• Reason for selecting a specific methodology —explain why this methodology is the most suitable to answer your research problem.
• Research instruments —explain the research instruments you plan to use, mainly referring to the data collection methods such as interviews, surveys, etc. Here as well, a reason should be mentioned for selecting the particular instrument.
• Sampling —this involves selecting a representative subset of the population being studied.
• Data collection —involves gathering data using several data collection methods, such as surveys, interviews, etc.
• Data analysis —describe the data analysis methods you will use once you’ve collected the data.
• Research limitations —mention any limitations you foresee while conducting your research.
• Validity and reliability —validity helps identify the accuracy and truthfulness of the findings; reliability refers to the consistency and stability of the results over time and across different conditions.
• Ethical considerations —research should be conducted ethically. The considerations include obtaining consent from participants, maintaining confidentiality, and addressing conflicts of interest.

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Frequently Asked Questions

Q1. What are the key components of research methodology?

A1. A good research methodology has the following key components:

• Research design
• Data collection procedures
• Data analysis methods
• Ethical considerations

Q2. Why is ethical consideration important in research methodology?

A2. Ethical consideration is important in research methodology to ensure the readers of the reliability and validity of the study. Researchers must clearly mention the ethical norms and standards followed during the conduct of the research and also mention if the research has been cleared by any institutional board. The following 10 points are the important principles related to ethical considerations: 10

• Participants should not be subjected to harm.
• Respect for the dignity of participants should be prioritized.
• Full consent should be obtained from participants before the study.
• Participants’ privacy should be ensured.
• Confidentiality of the research data should be ensured.
• Anonymity of individuals and organizations participating in the research should be maintained.
• The aims and objectives of the research should not be exaggerated.
• Affiliations, sources of funding, and any possible conflicts of interest should be declared.
• Communication in relation to the research should be honest and transparent.
• Misleading information and biased representation of primary data findings should be avoided.

Q3. What is the difference between methodology and method?

A3. Research methodology is different from a research method, although both terms are often confused. Research methods are the tools used to gather data, while the research methodology provides a framework for how research is planned, conducted, and analyzed. The latter guides researchers in making decisions about the most appropriate methods for their research. Research methods refer to the specific techniques, procedures, and tools used by researchers to collect, analyze, and interpret data, for instance surveys, questionnaires, interviews, etc.

Research methodology is, thus, an integral part of a research study. It helps ensure that you stay on track to meet your research objectives and answer your research questions using the most appropriate data collection and analysis tools based on your research design.

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• Research methodologies. Pfeiffer Library website. Accessed August 15, 2023. https://library.tiffin.edu/researchmethodologies/whatareresearchmethodologies
• Types of research methodology. Eduvoice website. Accessed August 16, 2023. https://eduvoice.in/types-research-methodology/
• The basics of research methodology: A key to quality research. Voxco. Accessed August 16, 2023. https://www.voxco.com/blog/what-is-research-methodology/
• Sampling methods: Types with examples. QuestionPro website. Accessed August 16, 2023. https://www.questionpro.com/blog/types-of-sampling-for-social-research/
• What is qualitative research? Methods, types, approaches, examples. Researcher.Life blog. Accessed August 15, 2023. https://researcher.life/blog/article/what-is-qualitative-research-methods-types-examples/
• What is quantitative research? Definition, methods, types, and examples. Researcher.Life blog. Accessed August 15, 2023. https://researcher.life/blog/article/what-is-quantitative-research-types-and-examples/
• Data analysis in research: Types & methods. QuestionPro website. Accessed August 16, 2023. https://www.questionpro.com/blog/data-analysis-in-research/#Data_analysis_in_qualitative_research
• Factors to consider while choosing the right research methodology. PhD Monster website. Accessed August 17, 2023. https://www.phdmonster.com/factors-to-consider-while-choosing-the-right-research-methodology/
• What is research methodology? Research and writing guides. Accessed August 14, 2023. https://paperpile.com/g/what-is-research-methodology/
• Ethical considerations. Business research methodology website. Accessed August 17, 2023. https://research-methodology.net/research-methodology/ethical-considerations/

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Research Methodologies

• What are research designs?

What are research methodologies?

Quantitative research methodologies, qualitative research methodologies, mixed method methodologies, selecting a methodology.

• What are research methods?
• Additional Sources

According to Dawson (2019),a research methodology is the primary principle that will guide your research.  It becomes the general approach in conducting research on your topic and determines what research method you will use. A research methodology is different from a research method because research methods are the tools you use to gather your data (Dawson, 2019).  You must consider several issues when it comes to selecting the most appropriate methodology for your topic.  Issues might include research limitations and ethical dilemmas that might impact the quality of your research.  Descriptions of each type of methodology are included below.

Quantitative research methodologies are meant to create numeric statistics by using survey research to gather data (Dawson, 2019).  This approach tends to reach a larger amount of people in a shorter amount of time.  According to Labaree (2020), there are three parts that make up a quantitative research methodology:

• Sample population
• How you will collect your data (this is the research method)
• How you will analyze your data

Once you decide on a methodology, you can consider the method to which you will apply your methodology.

Qualitative research methodologies examine the behaviors, opinions, and experiences of individuals through methods of examination (Dawson, 2019).  This type of approach typically requires less participants, but more time with each participant.  It gives research subjects the opportunity to provide their own opinion on a certain topic.

Examples of Qualitative Research Methodologies

• Action research:  This is when the researcher works with a group of people to improve something in a certain environment.  It is a common approach for research in organizational management, community development, education, and agriculture (Dawson, 2019).
• Ethnography:  The process of organizing and describing cultural behaviors (Dawson, 2019).  Researchers may immerse themselves into another culture to receive in "inside look" into the group they are studying.  It is often a time consuming process because the researcher will do this for a long period of time.  This can also be called "participant observation" (Dawson, 2019).
• Feminist research:  The goal of this methodology is to study topics that have been dominated by male test subjects.  It aims to study females and compare the results to previous studies that used male participants (Dawson, 2019).
• Grounded theory:  The process of developing a theory to describe a phenomenon strictly through the data results collected in a study.  It is different from other research methodologies where the researcher attempts to prove a hypothesis that they create before collecting data.  Popular research methods for this approach include focus groups and interviews (Dawson, 2019).

A mixed methodology allows you to implement the strengths of both qualitative and quantitative research methods.  In some cases, you may find that your research project would benefit from this.  This approach is beneficial because it allows each methodology to counteract the weaknesses of the other (Dawson, 2019).  You should consider this option carefully, as it can make your research complicated if not planned correctly.

What should you do to decide on a research methodology?  The most logical way to determine your methodology is to decide whether you plan on conducting qualitative or qualitative research.  You also have the option to implement a mixed methods approach.  Looking back on Dawson's (2019) five "W's" on the previous page , may help you with this process.  You should also look for key words that indicate a specific type of research methodology in your hypothesis or proposal.  Some words may lean more towards one methodology over another.

Quantitative Research Key Words

• How satisfied

Qualitative Research Key Words

• Experiences
• Thoughts/Think
• Relationship
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A tutorial on methodological studies: the what, when, how and why

Lawrence mbuagbaw.

1 Department of Health Research Methods, Evidence and Impact, McMaster University, Hamilton, ON Canada

2 Biostatistics Unit/FSORC, 50 Charlton Avenue East, St Joseph’s Healthcare—Hamilton, 3rd Floor Martha Wing, Room H321, Hamilton, Ontario L8N 4A6 Canada

3 Centre for the Development of Best Practices in Health, Yaoundé, Cameroon

Daeria O. Lawson

Livia puljak.

4 Center for Evidence-Based Medicine and Health Care, Catholic University of Croatia, Ilica 242, 10000 Zagreb, Croatia

David B. Allison

5 Department of Epidemiology and Biostatistics, School of Public Health – Bloomington, Indiana University, Bloomington, IN 47405 USA

Lehana Thabane

6 Departments of Paediatrics and Anaesthesia, McMaster University, Hamilton, ON Canada

7 Centre for Evaluation of Medicine, St. Joseph’s Healthcare-Hamilton, Hamilton, ON Canada

8 Population Health Research Institute, Hamilton Health Sciences, Hamilton, ON Canada

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Methodological studies – studies that evaluate the design, analysis or reporting of other research-related reports – play an important role in health research. They help to highlight issues in the conduct of research with the aim of improving health research methodology, and ultimately reducing research waste.

We provide an overview of some of the key aspects of methodological studies such as what they are, and when, how and why they are done. We adopt a “frequently asked questions” format to facilitate reading this paper and provide multiple examples to help guide researchers interested in conducting methodological studies. Some of the topics addressed include: is it necessary to publish a study protocol? How to select relevant research reports and databases for a methodological study? What approaches to data extraction and statistical analysis should be considered when conducting a methodological study? What are potential threats to validity and is there a way to appraise the quality of methodological studies?

Appropriate reflection and application of basic principles of epidemiology and biostatistics are required in the design and analysis of methodological studies. This paper provides an introduction for further discussion about the conduct of methodological studies.

The field of meta-research (or research-on-research) has proliferated in recent years in response to issues with research quality and conduct [ 1 – 3 ]. As the name suggests, this field targets issues with research design, conduct, analysis and reporting. Various types of research reports are often examined as the unit of analysis in these studies (e.g. abstracts, full manuscripts, trial registry entries). Like many other novel fields of research, meta-research has seen a proliferation of use before the development of reporting guidance. For example, this was the case with randomized trials for which risk of bias tools and reporting guidelines were only developed much later – after many trials had been published and noted to have limitations [ 4 , 5 ]; and for systematic reviews as well [ 6 – 8 ]. However, in the absence of formal guidance, studies that report on research differ substantially in how they are named, conducted and reported [ 9 , 10 ]. This creates challenges in identifying, summarizing and comparing them. In this tutorial paper, we will use the term methodological study to refer to any study that reports on the design, conduct, analysis or reporting of primary or secondary research-related reports (such as trial registry entries and conference abstracts).

In the past 10 years, there has been an increase in the use of terms related to methodological studies (based on records retrieved with a keyword search [in the title and abstract] for “methodological review” and “meta-epidemiological study” in PubMed up to December 2019), suggesting that these studies may be appearing more frequently in the literature. See Fig.  1 .

Trends in the number studies that mention “methodological review” or “meta-

epidemiological study” in PubMed.

The methods used in many methodological studies have been borrowed from systematic and scoping reviews. This practice has influenced the direction of the field, with many methodological studies including searches of electronic databases, screening of records, duplicate data extraction and assessments of risk of bias in the included studies. However, the research questions posed in methodological studies do not always require the approaches listed above, and guidance is needed on when and how to apply these methods to a methodological study. Even though methodological studies can be conducted on qualitative or mixed methods research, this paper focuses on and draws examples exclusively from quantitative research.

The objectives of this paper are to provide some insights on how to conduct methodological studies so that there is greater consistency between the research questions posed, and the design, analysis and reporting of findings. We provide multiple examples to illustrate concepts and a proposed framework for categorizing methodological studies in quantitative research.

What is a methodological study?

Any study that describes or analyzes methods (design, conduct, analysis or reporting) in published (or unpublished) literature is a methodological study. Consequently, the scope of methodological studies is quite extensive and includes, but is not limited to, topics as diverse as: research question formulation [ 11 ]; adherence to reporting guidelines [ 12 – 14 ] and consistency in reporting [ 15 ]; approaches to study analysis [ 16 ]; investigating the credibility of analyses [ 17 ]; and studies that synthesize these methodological studies [ 18 ]. While the nomenclature of methodological studies is not uniform, the intents and purposes of these studies remain fairly consistent – to describe or analyze methods in primary or secondary studies. As such, methodological studies may also be classified as a subtype of observational studies.

Parallel to this are experimental studies that compare different methods. Even though they play an important role in informing optimal research methods, experimental methodological studies are beyond the scope of this paper. Examples of such studies include the randomized trials by Buscemi et al., comparing single data extraction to double data extraction [ 19 ], and Carrasco-Labra et al., comparing approaches to presenting findings in Grading of Recommendations, Assessment, Development and Evaluations (GRADE) summary of findings tables [ 20 ]. In these studies, the unit of analysis is the person or groups of individuals applying the methods. We also direct readers to the Studies Within a Trial (SWAT) and Studies Within a Review (SWAR) programme operated through the Hub for Trials Methodology Research, for further reading as a potential useful resource for these types of experimental studies [ 21 ]. Lastly, this paper is not meant to inform the conduct of research using computational simulation and mathematical modeling for which some guidance already exists [ 22 ], or studies on the development of methods using consensus-based approaches.

When should we conduct a methodological study?

Methodological studies occupy a unique niche in health research that allows them to inform methodological advances. Methodological studies should also be conducted as pre-cursors to reporting guideline development, as they provide an opportunity to understand current practices, and help to identify the need for guidance and gaps in methodological or reporting quality. For example, the development of the popular Preferred Reporting Items of Systematic reviews and Meta-Analyses (PRISMA) guidelines were preceded by methodological studies identifying poor reporting practices [ 23 , 24 ]. In these instances, after the reporting guidelines are published, methodological studies can also be used to monitor uptake of the guidelines.

These studies can also be conducted to inform the state of the art for design, analysis and reporting practices across different types of health research fields, with the aim of improving research practices, and preventing or reducing research waste. For example, Samaan et al. conducted a scoping review of adherence to different reporting guidelines in health care literature [ 18 ]. Methodological studies can also be used to determine the factors associated with reporting practices. For example, Abbade et al. investigated journal characteristics associated with the use of the Participants, Intervention, Comparison, Outcome, Timeframe (PICOT) format in framing research questions in trials of venous ulcer disease [ 11 ].

How often are methodological studies conducted?

There is no clear answer to this question. Based on a search of PubMed, the use of related terms (“methodological review” and “meta-epidemiological study”) – and therefore, the number of methodological studies – is on the rise. However, many other terms are used to describe methodological studies. There are also many studies that explore design, conduct, analysis or reporting of research reports, but that do not use any specific terms to describe or label their study design in terms of “methodology”. This diversity in nomenclature makes a census of methodological studies elusive. Appropriate terminology and key words for methodological studies are needed to facilitate improved accessibility for end-users.

Why do we conduct methodological studies?

Methodological studies provide information on the design, conduct, analysis or reporting of primary and secondary research and can be used to appraise quality, quantity, completeness, accuracy and consistency of health research. These issues can be explored in specific fields, journals, databases, geographical regions and time periods. For example, Areia et al. explored the quality of reporting of endoscopic diagnostic studies in gastroenterology [ 25 ]; Knol et al. investigated the reporting of p -values in baseline tables in randomized trial published in high impact journals [ 26 ]; Chen et al. describe adherence to the Consolidated Standards of Reporting Trials (CONSORT) statement in Chinese Journals [ 27 ]; and Hopewell et al. describe the effect of editors’ implementation of CONSORT guidelines on reporting of abstracts over time [ 28 ]. Methodological studies provide useful information to researchers, clinicians, editors, publishers and users of health literature. As a result, these studies have been at the cornerstone of important methodological developments in the past two decades and have informed the development of many health research guidelines including the highly cited CONSORT statement [ 5 ].

Where can we find methodological studies?

Methodological studies can be found in most common biomedical bibliographic databases (e.g. Embase, MEDLINE, PubMed, Web of Science). However, the biggest caveat is that methodological studies are hard to identify in the literature due to the wide variety of names used and the lack of comprehensive databases dedicated to them. A handful can be found in the Cochrane Library as “Cochrane Methodology Reviews”, but these studies only cover methodological issues related to systematic reviews. Previous attempts to catalogue all empirical studies of methods used in reviews were abandoned 10 years ago [ 29 ]. In other databases, a variety of search terms may be applied with different levels of sensitivity and specificity.

Some frequently asked questions about methodological studies

In this section, we have outlined responses to questions that might help inform the conduct of methodological studies.

Q: How should I select research reports for my methodological study?

A: Selection of research reports for a methodological study depends on the research question and eligibility criteria. Once a clear research question is set and the nature of literature one desires to review is known, one can then begin the selection process. Selection may begin with a broad search, especially if the eligibility criteria are not apparent. For example, a methodological study of Cochrane Reviews of HIV would not require a complex search as all eligible studies can easily be retrieved from the Cochrane Library after checking a few boxes [ 30 ]. On the other hand, a methodological study of subgroup analyses in trials of gastrointestinal oncology would require a search to find such trials, and further screening to identify trials that conducted a subgroup analysis [ 31 ].

The strategies used for identifying participants in observational studies can apply here. One may use a systematic search to identify all eligible studies. If the number of eligible studies is unmanageable, a random sample of articles can be expected to provide comparable results if it is sufficiently large [ 32 ]. For example, Wilson et al. used a random sample of trials from the Cochrane Stroke Group’s Trial Register to investigate completeness of reporting [ 33 ]. It is possible that a simple random sample would lead to underrepresentation of units (i.e. research reports) that are smaller in number. This is relevant if the investigators wish to compare multiple groups but have too few units in one group. In this case a stratified sample would help to create equal groups. For example, in a methodological study comparing Cochrane and non-Cochrane reviews, Kahale et al. drew random samples from both groups [ 34 ]. Alternatively, systematic or purposeful sampling strategies can be used and we encourage researchers to justify their selected approaches based on the study objective.

Q: How many databases should I search?

A: The number of databases one should search would depend on the approach to sampling, which can include targeting the entire “population” of interest or a sample of that population. If you are interested in including the entire target population for your research question, or drawing a random or systematic sample from it, then a comprehensive and exhaustive search for relevant articles is required. In this case, we recommend using systematic approaches for searching electronic databases (i.e. at least 2 databases with a replicable and time stamped search strategy). The results of your search will constitute a sampling frame from which eligible studies can be drawn.

Alternatively, if your approach to sampling is purposeful, then we recommend targeting the database(s) or data sources (e.g. journals, registries) that include the information you need. For example, if you are conducting a methodological study of high impact journals in plastic surgery and they are all indexed in PubMed, you likely do not need to search any other databases. You may also have a comprehensive list of all journals of interest and can approach your search using the journal names in your database search (or by accessing the journal archives directly from the journal’s website). Even though one could also search journals’ web pages directly, using a database such as PubMed has multiple advantages, such as the use of filters, so the search can be narrowed down to a certain period, or study types of interest. Furthermore, individual journals’ web sites may have different search functionalities, which do not necessarily yield a consistent output.

Q: Should I publish a protocol for my methodological study?

A: A protocol is a description of intended research methods. Currently, only protocols for clinical trials require registration [ 35 ]. Protocols for systematic reviews are encouraged but no formal recommendation exists. The scientific community welcomes the publication of protocols because they help protect against selective outcome reporting, the use of post hoc methodologies to embellish results, and to help avoid duplication of efforts [ 36 ]. While the latter two risks exist in methodological research, the negative consequences may be substantially less than for clinical outcomes. In a sample of 31 methodological studies, 7 (22.6%) referenced a published protocol [ 9 ]. In the Cochrane Library, there are 15 protocols for methodological reviews (21 July 2020). This suggests that publishing protocols for methodological studies is not uncommon.

Authors can consider publishing their study protocol in a scholarly journal as a manuscript. Advantages of such publication include obtaining peer-review feedback about the planned study, and easy retrieval by searching databases such as PubMed. The disadvantages in trying to publish protocols includes delays associated with manuscript handling and peer review, as well as costs, as few journals publish study protocols, and those journals mostly charge article-processing fees [ 37 ]. Authors who would like to make their protocol publicly available without publishing it in scholarly journals, could deposit their study protocols in publicly available repositories, such as the Open Science Framework ( https://osf.io/ ).

Q: How to appraise the quality of a methodological study?

A: To date, there is no published tool for appraising the risk of bias in a methodological study, but in principle, a methodological study could be considered as a type of observational study. Therefore, during conduct or appraisal, care should be taken to avoid the biases common in observational studies [ 38 ]. These biases include selection bias, comparability of groups, and ascertainment of exposure or outcome. In other words, to generate a representative sample, a comprehensive reproducible search may be necessary to build a sampling frame. Additionally, random sampling may be necessary to ensure that all the included research reports have the same probability of being selected, and the screening and selection processes should be transparent and reproducible. To ensure that the groups compared are similar in all characteristics, matching, random sampling or stratified sampling can be used. Statistical adjustments for between-group differences can also be applied at the analysis stage. Finally, duplicate data extraction can reduce errors in assessment of exposures or outcomes.

Q: Should I justify a sample size?

A: In all instances where one is not using the target population (i.e. the group to which inferences from the research report are directed) [ 39 ], a sample size justification is good practice. The sample size justification may take the form of a description of what is expected to be achieved with the number of articles selected, or a formal sample size estimation that outlines the number of articles required to answer the research question with a certain precision and power. Sample size justifications in methodological studies are reasonable in the following instances:

• Comparing two groups
• Determining a proportion, mean or another quantifier
• Determining factors associated with an outcome using regression-based analyses

For example, El Dib et al. computed a sample size requirement for a methodological study of diagnostic strategies in randomized trials, based on a confidence interval approach [ 40 ].

Q: What should I call my study?

A: Other terms which have been used to describe/label methodological studies include “ methodological review ”, “methodological survey” , “meta-epidemiological study” , “systematic review” , “systematic survey”, “meta-research”, “research-on-research” and many others. We recommend that the study nomenclature be clear, unambiguous, informative and allow for appropriate indexing. Methodological study nomenclature that should be avoided includes “ systematic review” – as this will likely be confused with a systematic review of a clinical question. “ Systematic survey” may also lead to confusion about whether the survey was systematic (i.e. using a preplanned methodology) or a survey using “ systematic” sampling (i.e. a sampling approach using specific intervals to determine who is selected) [ 32 ]. Any of the above meanings of the words “ systematic” may be true for methodological studies and could be potentially misleading. “ Meta-epidemiological study” is ideal for indexing, but not very informative as it describes an entire field. The term “ review ” may point towards an appraisal or “review” of the design, conduct, analysis or reporting (or methodological components) of the targeted research reports, yet it has also been used to describe narrative reviews [ 41 , 42 ]. The term “ survey ” is also in line with the approaches used in many methodological studies [ 9 ], and would be indicative of the sampling procedures of this study design. However, in the absence of guidelines on nomenclature, the term “ methodological study ” is broad enough to capture most of the scenarios of such studies.

Q: Should I account for clustering in my methodological study?

A: Data from methodological studies are often clustered. For example, articles coming from a specific source may have different reporting standards (e.g. the Cochrane Library). Articles within the same journal may be similar due to editorial practices and policies, reporting requirements and endorsement of guidelines. There is emerging evidence that these are real concerns that should be accounted for in analyses [ 43 ]. Some cluster variables are described in the section: “ What variables are relevant to methodological studies?”

A variety of modelling approaches can be used to account for correlated data, including the use of marginal, fixed or mixed effects regression models with appropriate computation of standard errors [ 44 ]. For example, Kosa et al. used generalized estimation equations to account for correlation of articles within journals [ 15 ]. Not accounting for clustering could lead to incorrect p -values, unduly narrow confidence intervals, and biased estimates [ 45 ].

Q: Should I extract data in duplicate?

A: Yes. Duplicate data extraction takes more time but results in less errors [ 19 ]. Data extraction errors in turn affect the effect estimate [ 46 ], and therefore should be mitigated. Duplicate data extraction should be considered in the absence of other approaches to minimize extraction errors. However, much like systematic reviews, this area will likely see rapid new advances with machine learning and natural language processing technologies to support researchers with screening and data extraction [ 47 , 48 ]. However, experience plays an important role in the quality of extracted data and inexperienced extractors should be paired with experienced extractors [ 46 , 49 ].

Q: Should I assess the risk of bias of research reports included in my methodological study?

A : Risk of bias is most useful in determining the certainty that can be placed in the effect measure from a study. In methodological studies, risk of bias may not serve the purpose of determining the trustworthiness of results, as effect measures are often not the primary goal of methodological studies. Determining risk of bias in methodological studies is likely a practice borrowed from systematic review methodology, but whose intrinsic value is not obvious in methodological studies. When it is part of the research question, investigators often focus on one aspect of risk of bias. For example, Speich investigated how blinding was reported in surgical trials [ 50 ], and Abraha et al., investigated the application of intention-to-treat analyses in systematic reviews and trials [ 51 ].

Q: What variables are relevant to methodological studies?

A: There is empirical evidence that certain variables may inform the findings in a methodological study. We outline some of these and provide a brief overview below:

• Country: Countries and regions differ in their research cultures, and the resources available to conduct research. Therefore, it is reasonable to believe that there may be differences in methodological features across countries. Methodological studies have reported loco-regional differences in reporting quality [ 52 , 53 ]. This may also be related to challenges non-English speakers face in publishing papers in English.
• Authors’ expertise: The inclusion of authors with expertise in research methodology, biostatistics, and scientific writing is likely to influence the end-product. Oltean et al. found that among randomized trials in orthopaedic surgery, the use of analyses that accounted for clustering was more likely when specialists (e.g. statistician, epidemiologist or clinical trials methodologist) were included on the study team [ 54 ]. Fleming et al. found that including methodologists in the review team was associated with appropriate use of reporting guidelines [ 55 ].
• Source of funding and conflicts of interest: Some studies have found that funded studies report better [ 56 , 57 ], while others do not [ 53 , 58 ]. The presence of funding would indicate the availability of resources deployed to ensure optimal design, conduct, analysis and reporting. However, the source of funding may introduce conflicts of interest and warrant assessment. For example, Kaiser et al. investigated the effect of industry funding on obesity or nutrition randomized trials and found that reporting quality was similar [ 59 ]. Thomas et al. looked at reporting quality of long-term weight loss trials and found that industry funded studies were better [ 60 ]. Kan et al. examined the association between industry funding and “positive trials” (trials reporting a significant intervention effect) and found that industry funding was highly predictive of a positive trial [ 61 ]. This finding is similar to that of a recent Cochrane Methodology Review by Hansen et al. [ 62 ]
• Journal characteristics: Certain journals’ characteristics may influence the study design, analysis or reporting. Characteristics such as journal endorsement of guidelines [ 63 , 64 ], and Journal Impact Factor (JIF) have been shown to be associated with reporting [ 63 , 65 – 67 ].
• Study size (sample size/number of sites): Some studies have shown that reporting is better in larger studies [ 53 , 56 , 58 ].
• Year of publication: It is reasonable to assume that design, conduct, analysis and reporting of research will change over time. Many studies have demonstrated improvements in reporting over time or after the publication of reporting guidelines [ 68 , 69 ].
• Type of intervention: In a methodological study of reporting quality of weight loss intervention studies, Thabane et al. found that trials of pharmacologic interventions were reported better than trials of non-pharmacologic interventions [ 70 ].
• Interactions between variables: Complex interactions between the previously listed variables are possible. High income countries with more resources may be more likely to conduct larger studies and incorporate a variety of experts. Authors in certain countries may prefer certain journals, and journal endorsement of guidelines and editorial policies may change over time.

Q: Should I focus only on high impact journals?

A: Investigators may choose to investigate only high impact journals because they are more likely to influence practice and policy, or because they assume that methodological standards would be higher. However, the JIF may severely limit the scope of articles included and may skew the sample towards articles with positive findings. The generalizability and applicability of findings from a handful of journals must be examined carefully, especially since the JIF varies over time. Even among journals that are all “high impact”, variations exist in methodological standards.

Q: Can I conduct a methodological study of qualitative research?

A: Yes. Even though a lot of methodological research has been conducted in the quantitative research field, methodological studies of qualitative studies are feasible. Certain databases that catalogue qualitative research including the Cumulative Index to Nursing & Allied Health Literature (CINAHL) have defined subject headings that are specific to methodological research (e.g. “research methodology”). Alternatively, one could also conduct a qualitative methodological review; that is, use qualitative approaches to synthesize methodological issues in qualitative studies.

Q: What reporting guidelines should I use for my methodological study?

A: There is no guideline that covers the entire scope of methodological studies. One adaptation of the PRISMA guidelines has been published, which works well for studies that aim to use the entire target population of research reports [ 71 ]. However, it is not widely used (40 citations in 2 years as of 09 December 2019), and methodological studies that are designed as cross-sectional or before-after studies require a more fit-for purpose guideline. A more encompassing reporting guideline for a broad range of methodological studies is currently under development [ 72 ]. However, in the absence of formal guidance, the requirements for scientific reporting should be respected, and authors of methodological studies should focus on transparency and reproducibility.

Q: What are the potential threats to validity and how can I avoid them?

A: Methodological studies may be compromised by a lack of internal or external validity. The main threats to internal validity in methodological studies are selection and confounding bias. Investigators must ensure that the methods used to select articles does not make them differ systematically from the set of articles to which they would like to make inferences. For example, attempting to make extrapolations to all journals after analyzing high-impact journals would be misleading.

Many factors (confounders) may distort the association between the exposure and outcome if the included research reports differ with respect to these factors [ 73 ]. For example, when examining the association between source of funding and completeness of reporting, it may be necessary to account for journals that endorse the guidelines. Confounding bias can be addressed by restriction, matching and statistical adjustment [ 73 ]. Restriction appears to be the method of choice for many investigators who choose to include only high impact journals or articles in a specific field. For example, Knol et al. examined the reporting of p -values in baseline tables of high impact journals [ 26 ]. Matching is also sometimes used. In the methodological study of non-randomized interventional studies of elective ventral hernia repair, Parker et al. matched prospective studies with retrospective studies and compared reporting standards [ 74 ]. Some other methodological studies use statistical adjustments. For example, Zhang et al. used regression techniques to determine the factors associated with missing participant data in trials [ 16 ].

With regard to external validity, researchers interested in conducting methodological studies must consider how generalizable or applicable their findings are. This should tie in closely with the research question and should be explicit. For example. Findings from methodological studies on trials published in high impact cardiology journals cannot be assumed to be applicable to trials in other fields. However, investigators must ensure that their sample truly represents the target sample either by a) conducting a comprehensive and exhaustive search, or b) using an appropriate and justified, randomly selected sample of research reports.

Even applicability to high impact journals may vary based on the investigators’ definition, and over time. For example, for high impact journals in the field of general medicine, Bouwmeester et al. included the Annals of Internal Medicine (AIM), BMJ, the Journal of the American Medical Association (JAMA), Lancet, the New England Journal of Medicine (NEJM), and PLoS Medicine ( n  = 6) [ 75 ]. In contrast, the high impact journals selected in the methodological study by Schiller et al. were BMJ, JAMA, Lancet, and NEJM ( n  = 4) [ 76 ]. Another methodological study by Kosa et al. included AIM, BMJ, JAMA, Lancet and NEJM ( n  = 5). In the methodological study by Thabut et al., journals with a JIF greater than 5 were considered to be high impact. Riado Minguez et al. used first quartile journals in the Journal Citation Reports (JCR) for a specific year to determine “high impact” [ 77 ]. Ultimately, the definition of high impact will be based on the number of journals the investigators are willing to include, the year of impact and the JIF cut-off [ 78 ]. We acknowledge that the term “generalizability” may apply differently for methodological studies, especially when in many instances it is possible to include the entire target population in the sample studied.

Finally, methodological studies are not exempt from information bias which may stem from discrepancies in the included research reports [ 79 ], errors in data extraction, or inappropriate interpretation of the information extracted. Likewise, publication bias may also be a concern in methodological studies, but such concepts have not yet been explored.

A proposed framework

In order to inform discussions about methodological studies, the development of guidance for what should be reported, we have outlined some key features of methodological studies that can be used to classify them. For each of the categories outlined below, we provide an example. In our experience, the choice of approach to completing a methodological study can be informed by asking the following four questions:

• What is the aim?

A methodological study may be focused on exploring sources of bias in primary or secondary studies (meta-bias), or how bias is analyzed. We have taken care to distinguish bias (i.e. systematic deviations from the truth irrespective of the source) from reporting quality or completeness (i.e. not adhering to a specific reporting guideline or norm). An example of where this distinction would be important is in the case of a randomized trial with no blinding. This study (depending on the nature of the intervention) would be at risk of performance bias. However, if the authors report that their study was not blinded, they would have reported adequately. In fact, some methodological studies attempt to capture both “quality of conduct” and “quality of reporting”, such as Richie et al., who reported on the risk of bias in randomized trials of pharmacy practice interventions [ 80 ]. Babic et al. investigated how risk of bias was used to inform sensitivity analyses in Cochrane reviews [ 81 ]. Further, biases related to choice of outcomes can also be explored. For example, Tan et al investigated differences in treatment effect size based on the outcome reported [ 82 ].

Methodological studies may report quality of reporting against a reporting checklist (i.e. adherence to guidelines) or against expected norms. For example, Croituro et al. report on the quality of reporting in systematic reviews published in dermatology journals based on their adherence to the PRISMA statement [ 83 ], and Khan et al. described the quality of reporting of harms in randomized controlled trials published in high impact cardiovascular journals based on the CONSORT extension for harms [ 84 ]. Other methodological studies investigate reporting of certain features of interest that may not be part of formally published checklists or guidelines. For example, Mbuagbaw et al. described how often the implications for research are elaborated using the Evidence, Participants, Intervention, Comparison, Outcome, Timeframe (EPICOT) format [ 30 ].

Sometimes investigators may be interested in how consistent reports of the same research are, as it is expected that there should be consistency between: conference abstracts and published manuscripts; manuscript abstracts and manuscript main text; and trial registration and published manuscript. For example, Rosmarakis et al. investigated consistency between conference abstracts and full text manuscripts [ 85 ].

In addition to identifying issues with reporting in primary and secondary studies, authors of methodological studies may be interested in determining the factors that are associated with certain reporting practices. Many methodological studies incorporate this, albeit as a secondary outcome. For example, Farrokhyar et al. investigated the factors associated with reporting quality in randomized trials of coronary artery bypass grafting surgery [ 53 ].

Methodological studies may also be used to describe methods or compare methods, and the factors associated with methods. Muller et al. described the methods used for systematic reviews and meta-analyses of observational studies [ 86 ].

Some methodological studies synthesize results from other methodological studies. For example, Li et al. conducted a scoping review of methodological reviews that investigated consistency between full text and abstracts in primary biomedical research [ 87 ].

Some methodological studies may investigate the use of names and terms in health research. For example, Martinic et al. investigated the definitions of systematic reviews used in overviews of systematic reviews (OSRs), meta-epidemiological studies and epidemiology textbooks [ 88 ].

In addition to the previously mentioned experimental methodological studies, there may exist other types of methodological studies not captured here.

• 2. What is the design?

Most methodological studies are purely descriptive and report their findings as counts (percent) and means (standard deviation) or medians (interquartile range). For example, Mbuagbaw et al. described the reporting of research recommendations in Cochrane HIV systematic reviews [ 30 ]. Gohari et al. described the quality of reporting of randomized trials in diabetes in Iran [ 12 ].

Some methodological studies are analytical wherein “analytical studies identify and quantify associations, test hypotheses, identify causes and determine whether an association exists between variables, such as between an exposure and a disease.” [ 89 ] In the case of methodological studies all these investigations are possible. For example, Kosa et al. investigated the association between agreement in primary outcome from trial registry to published manuscript and study covariates. They found that larger and more recent studies were more likely to have agreement [ 15 ]. Tricco et al. compared the conclusion statements from Cochrane and non-Cochrane systematic reviews with a meta-analysis of the primary outcome and found that non-Cochrane reviews were more likely to report positive findings. These results are a test of the null hypothesis that the proportions of Cochrane and non-Cochrane reviews that report positive results are equal [ 90 ].

• 3. What is the sampling strategy?

Methodological reviews with narrow research questions may be able to include the entire target population. For example, in the methodological study of Cochrane HIV systematic reviews, Mbuagbaw et al. included all of the available studies ( n  = 103) [ 30 ].

Many methodological studies use random samples of the target population [ 33 , 91 , 92 ]. Alternatively, purposeful sampling may be used, limiting the sample to a subset of research-related reports published within a certain time period, or in journals with a certain ranking or on a topic. Systematic sampling can also be used when random sampling may be challenging to implement.

• 4. What is the unit of analysis?

Many methodological studies use a research report (e.g. full manuscript of study, abstract portion of the study) as the unit of analysis, and inferences can be made at the study-level. However, both published and unpublished research-related reports can be studied. These may include articles, conference abstracts, registry entries etc.

Some methodological studies report on items which may occur more than once per article. For example, Paquette et al. report on subgroup analyses in Cochrane reviews of atrial fibrillation in which 17 systematic reviews planned 56 subgroup analyses [ 93 ].

This framework is outlined in Fig.  2 .

A proposed framework for methodological studies

Conclusions

Methodological studies have examined different aspects of reporting such as quality, completeness, consistency and adherence to reporting guidelines. As such, many of the methodological study examples cited in this tutorial are related to reporting. However, as an evolving field, the scope of research questions that can be addressed by methodological studies is expected to increase.

In this paper we have outlined the scope and purpose of methodological studies, along with examples of instances in which various approaches have been used. In the absence of formal guidance on the design, conduct, analysis and reporting of methodological studies, we have provided some advice to help make methodological studies consistent. This advice is grounded in good contemporary scientific practice. Generally, the research question should tie in with the sampling approach and planned analysis. We have also highlighted the variables that may inform findings from methodological studies. Lastly, we have provided suggestions for ways in which authors can categorize their methodological studies to inform their design and analysis.

Acknowledgements

Abbreviations, authors’ contributions.

LM conceived the idea and drafted the outline and paper. DOL and LT commented on the idea and draft outline. LM, LP and DOL performed literature searches and data extraction. All authors (LM, DOL, LT, LP, DBA) reviewed several draft versions of the manuscript and approved the final manuscript.

This work did not receive any dedicated funding.

Availability of data and materials

Ethics approval and consent to participate.

Not applicable.

Consent for publication

Competing interests.

DOL, DBA, LM, LP and LT are involved in the development of a reporting guideline for methodological studies.

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Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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FAQ: Research Design & Method

What is the difference between Research Design and Research Method?

Research design is a plan to answer your research question.  A research method is a strategy used to implement that plan.  Research design and methods are different but closely related, because good research design ensures that the data you obtain will help you answer your research question more effectively.

Which research method should I choose ?

It depends on your research goal.  It depends on what subjects (and who) you want to study.  Let's say you are interested in studying what makes people happy, or why some students are more conscious about recycling on campus.  To answer these questions, you need to make a decision about how to collect your data.  Most frequently used methods include:

• Observation / Participant Observation
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• Secondary Data Analysis / Archival Study
• Mixed Methods (combination of some of the above)

One particular method could be better suited to your research goal than others, because the data you collect from different methods will be different in quality and quantity.   For instance, surveys are usually designed to produce relatively short answers, rather than the extensive responses expected in qualitative interviews.

What other factors should I consider when choosing one method over another?

Time for data collection and analysis is something you want to consider.  An observation or interview method, so-called qualitative approach, helps you collect richer information, but it takes time.  Using a survey helps you collect more data quickly, yet it may lack details.  So, you will need to consider the time you have for research and the balance between strengths and weaknesses associated with each method (e.g., qualitative vs. quantitative).

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• Last Updated: Aug 21, 2023 10:42 AM

Top 5 Key Differences Between Methods and Methodology

While burning the midnight oil during literature review , most researchers do not realize that the methods and methodology section forms the spine of their research. Researchers use a systematic foundation to conduct research by implementing methods. Methods are strategies, tools, and techniques, which are often confused with methodology that consists of a systematic and theoretical analysis of the research methods. The difference between methods and methodology needs to be well understood while documenting your research .

What is Methods and Methodology?

Researchers implement systematic methods to conduct a research. They define the research topic to establish a deeper and clearer understanding in the methods section. Furthermore, methods consist of all techniques, strategies, and tools employed by a researcher to complete the experiment and find solution to the research problem.

However, methodology is a systematic and theoretical approach to collect and evaluate data throughout the research process. It allows researchers to validate a study’s rigor to acquire new information. The purpose of research methodology is to prove the credibility, validity, and reliability of a chosen research method.

Objective of Methods and Methodology

While the methods section is just a research tool or a component of research, methodology is the justification for using a particular research method.

The objective of research methods is to provide thorough information of research design , participants, equipment, materials, variables, and procedures. It must allow other researchers to reproduce similar results based on the documented methods. Whereas, the objective of research methodology is to determine the accuracy and efficiency of the methods opted by the researchers for a particular experiment.

How to Write Methods and Methodology Section of a Research Paper?

Most researchers are commonly asked to re-write the methods and methodology section as there exists an ambiguity in the understanding of these elements. One should understand that incorrectness in these sections may lead to repercussions which are uncalled for. A clear knowledge of methods and methodologies employed in research will also make your process of reviewing and understanding other literature easier. A robust method and methodology section is a point of validation for authentic research.

While writing the methods section you must remember the following:

• Authors must duly cite all sources that helped them in selecting the methods for the research study. Furthermore, it should also include parameters of past studies must to indicate relevance with the current study.
• It is mandatory to cite the sources of all participants of the study. The details of participants such as geographical location, age, sex, their initial conditions, etc. must be mentioned in the methods section.
• The methods section must also include the inclusion and exclusion criteria of subjects.
• Description of division of chosen group and their characteristics is also an element of the methods section.
• The methods section must also include the study design. Necessary preparations, software used, and instruments must be explained here.
• Finally, it must include statistical analyses. For example: type of data, their measurements, and statistical tests.

Methodology

A well-written methodology section must include the following:

• An introduction and explanation of reasons for the systematic methodological approach (qualitative, quantitative, or mixed method) used throughout the research process.
• The methodology section must indicate the applicability, validity, and credibility of all methods applied in the research.
• It must clearly describe specific data collation methods and provide detailed explanation of data analysis.
• Lastly, the methodology section must justify rationale for chosen research methods and procedures.

What are the Key Differences between Methods and Methodology?

These key points clearly establishes the difference between often mistaken methods and methodology section:

To summarize, we shall say that a technique is far more specific than a method and a method is far more specific than the methodology. It’s beyond listing steps of experiment or audit trails that you follow to find solution to your research problem. With one methodology, you can apply several methods to support or reject the research hypothesis . In conclusion, we can say that both methods and methodologies are an important part of research and are related to each other’s existence.

How to write the broader strategy for the approach to find solution to the problem? When did you realize the difference between methods and methodology of research? How do you structure your methods and methodology section of your research papers? Moreover, did you have to rewrite the methods and methodology section? Share your experience with us in the comments section below! You can also visit our Q&A forum  for frequently asked questions related to different aspects of research writing and publishing answered by our team that comprises subject-matter experts, eminent researchers, and publication experts.

Frequently Asked Questions

Research methodology is a systematic and theoretical approach to collect and evaluate data throughout the research process. Research method consists of all techniques, strategies, and tools employed by a researcher to complete the experiment and find solution to a research problem.

The difference between research method and methodology are: • A research method is used to find solution to the research problem. On the other hand, a research methodology determines the appropriateness of the methods applied with a view to ascertain solution. • Research methodologies are applied in the initial stages of the research; while research method is employed in the later stages of the study. • Research methods encompass the strategies to accomplish the research objectives; while methodologies include the different techniques to carry out investigation in the study.

Research methodology is a systematic and theoretical approach to collect and evaluate data throughout the research process.

The types of research methods are: • Applied research: Applied Research is used to address issues on different sectors. • Fundamental research: Fundamental research is employed to formulate a theory on a particular natural phenomenon or explore an existing concept to supplement it with further information. • Descriptive research: Descriptive Research focuses on describing the facts and is used when the research aims to understand the characteristics or trends. • Analytical research: Analytical Research focuses on the evaluation and interpretation of the given data. • Quantitative research: Quantitative research measures a particular amount or quantity, and focuses on gathering and interpreting numerical data for making predictions. • Qualitative research: Qualitative research understands the quality of a certain phenomenon or studies the details of a certain topic. • Empirical research: Empirical research deals with observation through experiments, without focusing on the theory or system. • Conceptual research: Conceptual research is related to an abstract idea or a topic to develop a new concept by observing the existing information on a topic without any practical experiments.

The 4 types of research methodology are: • Quantitative research methodology: Quantitative research methodology deals with quantifying a certain data to obtain results. • Qualitative research methodology: Qualitative research focuses on the non-numerical data that deals with the qualitative information of the topic. • Experimental research methodology: Experimental research methodology examines the interaction of the selected variables and observes their effects upon manipulation with the help of experimental techniques. • Case-study research methodology: Case-study research methodology deals with the contextual information to gain an in-depth idea regarding a certain topic.

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Difference Between Research Method and Research Methodology

The research methods are often confused with research methodology , which implies the scientific analysis of the research methods, so as to find a solution to the problem at hand. Hence, it seems apt to clarify the differences between research method and research methodology at this juncture, have a look.

Content: Research Method Vs Research Methodology

Comparison chart, definition of research method.

Research method pertains to all those methods, which a researcher employs to undertake research process, to solve the given problem. The techniques and procedure, that are applied during the course of studying research problem are known as the research method. It encompasses both qualitative and quantitative method of performing research operations, such as survey, case study, interview, questionnaire, observation, etc.

These are the approaches, which help in collecting data and conducting research, in order to achieve specific objectives such as theory testing or development. All the instruments and behaviour, used at various levels of the research activity such as making observations, data collection, data processing, drawing inferences, decision making, etc. are included in it. Research methods are put into three categories:

• First Category : The methods relating to data collection are covered. Such methods are used when the existing data is not sufficient, to reach the solution.
• Second Category: Incorporates the processes of analysing data, i.e. to identify patterns and establish a relationship between data and unknowns.
• Third Category : Comprise of the methods which are used to check the accuracy of the results obtained.

Definition of Research Methodology

Research Methodology, as its name suggest is the study of methods, so as to solve the research problem. It is the science of learning the way research should be performed systematically. It refers to the rigorous analysis of the methods applied in the stream of research, to ensure that the conclusions drawn are valid, reliable and credible too.

The researcher takes an overview of various steps that are chosen by him in understanding the problem at hand, along with the logic behind the methods employed by the researcher during study. It also clarifies the reason for using a particular method or technique, and not others, so that the results obtained can be assessed either by the researcher himself or any other party.

Key Differences Between Research Method and Research Methodology

The differences between research method and research methodology can be drawn clearly on the following grounds:

• The research method is defined as the procedure or technique applied by the researcher to undertake research. On the other hand, research methodology is a system of methods, used scientifically for solving the research problem.
• The research method is nothing but the behaviour or tool, employed in selecting and building research technique. Conversely, research methodology implies the science of analysing, the manner in which research is conducted appropriately.
• The research method is concerned with carrying out experiment, test, surveys, interviews, etc. As against this, research methodology is concerned with learning various techniques which can be employed in the performance of experiment, test or survey.
• Research method covers various investigation techniques. Unlike, research methodology, which consists of complete approach aligned towards the attainment of purpose.
• Research method intends to discover the solution to the problem at hand. In contrast, research methodology aspires to apply appropriate procedures, with a view to ascertaining solutions.

The scope of research methodology is wider than that of research method, as the latter is the part of the former. For understanding the research problem thoroughly, the researcher should know the research methodology along with the methods.

In a nutshell, research method refers to the technique which can be adopted to explore the nature of the world that surrounds us. On the contrary, research methodology is the foundation, which helps us to understand the determinants influencing the effectiveness of the methods applied.

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“Difference Between Research Method and Research Methodology” Keydifferences.com By Surbhi S. 28 Feb 2018 https://keydifferences.com/difference-between-research-method-and-research-methodology.html >

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UCF Alumnus Brings Focus to High-powered Laser Delivery Research

UCF College of Optics and Photonics (CREOL) researcher and Professor Rodrigo Amezcua Correa and his doctoral graduate Matthew Cooper tested and studied an emerging method of high-power laser delivery using a hollow-core fiber.

By Eddy Duryea ’13 | May 29, 2024

Recently realized UCF results published in the journal Optica could lead to a new generation of fiber-based laser beam delivery systems with applications in directed energy, precision machining, medical sciences and power beaming over fiber.

Matthew Cooper, who completed his optics and photonics doctorate from CREOL , tested the power, efficiency and quality of laser transmission via a hollow-core fiber just prior to his graduation in late 2023.

Hollow-core fibers are special types of optical fibers that look a bit like a straw, with a tiny hole running through the middle. They can transmit light faster and with less distortion than commonly used solid-core fibers, making them important for artificial intelligence, data centers, laser technology, and medical devices.

However, the widespread application has been limited by needs for more research and development.

That’s where Amezcua and Cooper’s research comes in. Their study demonstrated the successful transmission of high-power laser beams through gas-filled, reduced distortion (antiresonant) hollow-core fibers. The researchers achieved a record 2.2 kW of laser power through a single-mode (one path) antiresonant hollow-core fiber with remarkable efficiency and beam quality. Until now, the transmission of precise wavelength (narrow-linewidth) single-mode lasers at multi-kW power levels through a hollow-core fiber was not yet achieved.

The findings provide critical data in the emerging field of laser transmission with implications for directed energy and enhanced optical communications, Cooper says.

“The results of this particular experiment proved out the ability for these types of fiber structure to handle such extreme powers,” he says.

Applying the Research

Cooper says he believes hollow-core fiber research is on the precipice of addressing critical needs in communications and high-power lasers, and he is intrigued by them potentially being adopted on a larger scale.

“We need long distance transmission lines,” Cooper says. “In solid core fiber, there are nonlinear effects, which accumulate over long distance and distort and disrupt optical characteristics.”

Concentrated high-power lasers for use in industrial, medical or defense applications also may benefit from hollow-core fiber delivery, he says.

Precision and Focus

Most optical fibers are solid core, meaning the core surrounding the light transmission is made entirely of a single material like glass. Generally, they are easy to manufacture and are widely used in communications or laser applications. However, they are susceptible to disruption or scattering at higher power levels.

Hollow-core fibers, on the other hand, are filled with gasses to accommodate high power output, which helps them deliver and maintain laser power levels.

“This was a prototype fiber we fabricated within the fiber draw tower at UCF CREOL, where the structure was never tested at these levels before,” Cooper says.

For the tests, the hollow core was filled with atmospheric air, and the results showed potential advantages over the solid core fibers.

The experiment consisted of testing two hollow-core fiber lengths at various linewidths while carefully increasing the power in increments of 220 watts at a time to monitor the stability and efficiency of the power delivery. The laser ultimately was stabilized and observed at 2.2 kW – which previously had not been achieved.

A high level of precision and vigilance was necessary when dealing with lasers operating at 500,000 times greater intensity than that of a common laser pointer, Cooper says.

“I was truly excited when we first reached these results because we just didn’t know what would happen at these power levels,” Cooper says. “When working in this regime, any slight misalignment or piece of dust in the optics could quite literally cause a fire and ruin your whole experiments or thousands of dollars of equipment if not extremely careful.”

Overall, the experiments were hailed as a success as they demonstrated the hollow-core fiber’s suitability for high-power transmission, provided valuable performance metrics, and explored nonlinearity effects for potential applications.

The Next Steps

Cooper is stationed in South Korea as part of his active service in the Space Force, but he plans to put his expanding optics knowledge to work as a professor at the Air Force Institute of Technology upon return.

He’s hopeful that he and his former colleagues at CREOL will keep cultivating hollow-core laser delivery methods and helping to realize their potential.

“The first step is to keep pushing the power limits of UCF’s hollow-core fiber designs,” Cooper says. “In theory, the fiber should handle power levels well beyond what the coupling optics could ever handle. Secondly, the previous result about rotational Raman shifting [working at different wavelengths] has opened a brand-new door for potential laser sources. By tailoring the source wavelength, the gases inside the fiber, and the fiber design, we should be able to generate a multi kW class laser at any wavelength between 1um and 5um, which has never been done for most frequencies of light within that range.”

UCF will continue studying the limitations and properties of hollow-core fibers, says Amezcua, who also served as research advisor to Cooper.

“We have been working on hollow-core fibers for almost 20 years,” Amezcua says. “We don’t yet understand the limits, and it is a very new regime for light.”

The focus on hollow-core fibers signals a shift in focus in optics and an opportunity to expand the field of communications and high-powered lasers, he says.

“Basically, we were doing things you cannot do with any other conventional fibers,” Amezcua says. “They’re quite remarkable. It opens up possibilities that weren’t available before. There is a lot of interest for many areas of applications.”

The results of Cooper’s experiments are a big step forward for optics research, he says. Cooper spent nearly three years pursuing his Ph. D. with CREOL, and he had achieved many unique results in that time, Amezcua says.

“We are able to expand these kinds of experiments now,” he says. “We have a few news students who have come on recently to continue working on this and we’re hoping to become one of the leading places for hollow core fibers here at UCF.”

UCF CREOL researcher and professor Axel Schülzgen also served in an advisory role for this research. UCF CREOL research scientist Jose Enrique Antonio-Lopez and post-doctoral researcher Stephanos Yerolatsitis fabricated the prototype fibers while UCF post-doctoral scholar Daniel Cruz-Delgado and research associate professor Ivan Divliansky provided support for equipment and analysis techniques. Cooper’s fellow UCF students Joseph Wallen and Dan Parra assisted in conducting and recording experiments.

Researchers from Coherent Corp. and the Florida Institute of Technology also contributed to the study.

Researchers’ Credentials

Amezcua joined CREOL and the Townes Laser Institute in 2011. He obtained his doctoral degree from the Optoelectronics Research Centre at the University of Southampton where he researched the development of photonic crystal fibers.

Cooper earned his doctoral degree from UCF in December of 2023. He currently is serving as an officer in Space Force after joining the Air Force at 17 years old. Cooper received two master’s degrees in electrical engineering and aeronautical engineering from the Air Force Institute of Technology. He also earned an MBA from the University of South Dakota and his bachelor’s in electrical engineering from the Pennsylvania State University.

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A review of the environments, biota, and methods used in microplastics research in South Africa

• Heinrich T.J. Dahms Department of Zoology, University of Johannesburg, Johannesburg, South Africa https://orcid.org/0000-0002-0199-5199
• Richard Greenfield Department of Zoology, University of Johannesburg, Johannesburg, South Africa https://orcid.org/0000-0002-4329-3566

Microplastics are small plastic materials often defined as those between 5 mm and 0.05 mm in size. Microplastics can have toxicological impacts on various biota, from gut blockages to the transport or leaching of toxicants used in their production or absorbed from the surrounding environment. Although microplastic research has increased significantly, microplastic research in Africa lags behind that of developed countries. South Africa is the African nation with the highest number of microplastic publications. We aimed to determine the current state of microplastic research in South Africa. A total of 46 publications on microplastics in South Africa have been produced. However, many of these publications use methods that might not be accurate in determining holistic descriptions of microplastics in the aquatic environment. Similarly, many ecologically relevant environments and species have not been investigated for microplastics in the country, including any atmospheric or terrestrial environment. We conclude that, although the research being produced in South Africa can be considered adequate, a singular standard method for sampling and assessing microplastics in South African environments is required. The production of such a standard method would be critical to use as a monitoring tool to determine and compare microplastic abundances across the country and globally.

Significance:

• More than 40 publications on microplastics have been produced in South Africa.
• Microplastics have been discovered in multiple aquatic environments in South Africa, but have not been investigated in atmospheric or terrestrial environments.
• Polymer analysis was limited in published research.
• A standard method is required for comparing between studies.
• Terrestrial and atmospheric microplastic studies are required.

Additional Files

• Peer review history

How to Cite

• Endnote/Zotero/Mendeley (RIS)

Copyright is retained by the authors. Readers are welcome to reproduce, share and adapt the content without permission provided the source is attributed.

Disclaimer: The publisher and editors accept no responsibility for statements made by the authors

Funding data

• National Research Foundation Grant numbers MND200505519919;37999

Research on the theory and method of reduced-hole blasting for large cross-section tunnel based on explosive energy dissipation

• Open access
• Published: 28 May 2024
• Volume 10 , article number  96 , ( 2024 )

Cite this article

You have full access to this open access article

• Xingchao Tian 1 ,
• Tiejun Tao 2 &
• Caijin Xie 1  

The traditional tunnel drilling and blasting method places cut holes at the lower center of the excavation face, resulting in an excessive number of blasting holes. With the continuous increase in cross-section area, this design concept can no longer meet the requirements of safe and efficient tunnel boring for large cross-section tunnels. This paper puts forward the theory and method of reduced-hole blasting for large cross-section tunnels, as an alternative to the traditional drilling and blasting method of the “more holes, less charge” design concept. Based on the explosion energy dissipation law and rock’s critical crushing energy dissipation characteristics, the calculation method of the extrapolation distance of the wedge-cut holes is given. The optimum extrapolation distance of the wedge-cut holes was verified using numerical simulation and field tests. The results show that the number of drilling holes can be reduced by about 15.8% using the theory and method proposed in this paper, and at the same time, the damage of retained rock can be effectively controlled. The results of this study can provide a reference for the design of blast network parameters for similar large cross-section tunnels.

Article Highlights

This paper put forward the theory and method of reduced hole blasting (RHB) for large cross section tunnels, the number of blasting holes was reduced by an average of 15.8%.

This paper gave the wedge-cut hole extrapolation distance calculation method based on the explosion energy dissipation law and rock’s critical crushing energy dissipation characteristics.

This paper proposed a computational expression for energy dissipation under coupled in-situ stress and blast loading, determined the critical crushing energy dissipation density of gray sandstone under different combined dynamic and static loading conditions.

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Avoid common mistakes on your manuscript.

1 Introduction

The drilling and blasting method has the advantages of being economic and efficient, and is currently the most commonly used construction method for highway and railroad tunnels, mine shafts, and underground space hard rock excavation. With China’s socio-economic development, as well as the continuous promotion of the Belt and Road initiative and the construction of new infrastructure, large cross-section tunnels have appeared frequently. However, the design of blasting parameters still follows the traditional design concept of small cross-section tunnels, resulting in too many blasting holes, which restricts the quality and duration of tunnel construction. Therefore, there is an urgent need to put forward an innovative theory and method of hole-reduction blasting for large cross-section tunnels, to maximize the outward push of the wedge-cut holes, and to reduce the number of holes while ensuring the quality of blasting, so as to realize the safe and efficient blasting of large cross-section tunnels.

The parameter design of wedge-cut holes is the soul of whether large cross-section tunnels can be successfully blasted to break rocks. Many scholars have conducted research on the hollowing parameters of large cross-section tunnel blasting. Yang et al. ( 2024 ) showed that in large cross-section hard-rock tunnel blasting, using the frames on both sides of the drilling and blasting cart as a reference for the main wedge-cut holes can reduce the number of drilled holes, but the theoretical basis of this design method was not reflected in their study. Ji et al. ( 2020 ) proposed an inverted T-shaped hollowing and blasting method for very large cross-section tunnels, which improved the blasting effect. Mei et al. ( 2021 ) carried out studies on hollowing methods, blast hole placement, charge volume, and charge structure to achieve safe and efficient blasting excavation. Zhang et al. ( 2022 ) proposed an innovative hollowing and blasting technique based on cavity hollowing and debris throwing. Li et al. ( 2023 ) proposed a hollowing out and blasting technique with decentralized charging and staged blasting. Qin and Zhang ( 2020 ) proposed a “three-step + inverted” tunnel blasting excavation method, which effectively controlled the blasting vibration. Cheng et al. ( 2023 ) proposed a medium-deep hole-hollowing and blasting method based on directional pre-cracking with slit charging to improve the tunneling progress. Gao et al. ( 2022 ) improved the hollowing and blasting initiation method and proposed a hybrid initiation method based on the reverse transmission of neighboring holes. Zhang et al. ( 2020a ; b ) analyzed the hollow-hole effect of hollowing and blasting and gave a method for determining the parameters of hollow-hole straight-eye hollowing and blasting. Zhang et al. ( 2020a ; b ) proposed a second-order two-stage hollowing and blasting technique, which effectively improved the efficiency of blasting excavation. Wu et al. ( 2023 ) proposed a zonal blasting excavation scheme for small-spaced large-section tunnels to effectively control blasting vibration and perimeter rock damage. The above research has effectively improved the blasting quality and construction efficiency through the optimization of segmental hollowing blasting technology and hollowing parameters, which is of great significance for the safe and efficient blasting of large cross-section tunnels. However, its parameter design methods are not free from the traditional design concept of small cross-section roadway blasting, the number of blasting holes laid is still high. With the increasing cross-section area of the tunnel excavation, it is possible to extrapolate the placement position of the wedge-cut holes, and utilize the bidirectional critical surface formed after blasting the wedge-cut holes to break the rock effectively. The transformation of design concepts is crucial.

Currently, the wedge-cut holes spacing, angle, and other parameters are determined by the radius of the crushed zone, the radius of the fractured zone, and the geometric relationship, which leads to smaller spacing of the wedge-cut holes and limited hollowing effect. The accumulation, propagation, and dissipation of energy are the driving factors for the destabilization of the medium, and it is more scientific to determine the optimal spacing of the wedge-cut holes based on the explosive energy dissipation. Li et al. ( 2018a ; b ) analyzed the energy evolution law of deep buried tunnels under explosive loading. Leng et al. ( 2016 ) discussed the process of explosive energy transfer during side detonation and end detonation. Sanchidrián et al. ( 2007 ) analyzed the energy distribution pattern within the rock mass after explosive blasting based on single-hole blasting tests. Xia et al. ( 2020 ) analyzed the effect of charge structure on blast energy transfer. Leng et al. ( 2019 ) analyzed the explosion energy transfer law under the condition of double-point detonation in the hole. The above research has conducted a detailed exploration of the transmission and distribution of explosion energy, which is of great significance for exploring the mechanism of rock damage and failure. However, there are few research results on the design of hole network parameters for large cross-section tunnel blasting from the perspective of explosive energy dissipation.

This paper is based on the significant demand for safe and efficient tunnel boring in large cross-section tunnels, and offers the method of wedge-cut hole extrapolation, featuring additional center holes, and adjusts the detonation sequence of large cross-section tunnels according to reduced-hole blasting (RHB) theory and method, completely changing the traditional tunnel blasting "more holes, less charge" design concept. Based on the explosion energy dissipation law and the rock’s critical crushing energy dissipation characteristics, the calculation method of the extrapolation distance of the wedge-cut hole is given. A three-dimensional numerical simulation model was established to compare and analyze the hollowing effect and the damage law of the retained rock body after being subjected to different wedge-cut holes with different extrapolation distances, and the optimal extrapolation distance of the wedge-cut holes was determined. Based on the Gonghe Village Tunnel of the Ludian-Qiaojia Expressway, five on-site blasting tests were carried out to verify the scientific validity of the theory and method proposed in this paper. The results of this study can provide a reference for the design of blast network parameters for similar large cross-section tunnels.

2 Theory and method

2.1 engineering background.

The Gonghe Village Tunnel of the Ludian-Qiaojia Expressway is located in Chongxi Township, Qiaojia County, Yunnan Province. The total length of the right tunnel is 10,698 m, with a maximum depth of about 1320 m, which is a two-way four-lane detached extra-long tunnel. The buried depth of the section used in this study is about 400 m, the surrounding rock level is class III, the surrounding rock lithology is dominated by gray sandstone, and the excavated section area is 99.28 m 2 , which belongs to the large cross-section tunnel. The section used in this study was excavated by blasting using the upper and lower step method, as shown in Fig.  1 .

The Gonghe village tunnel

The originally proposed Gonghe Village Tunnel was constructed by using the traditional drilling and blasting method, which led to the problems of a large number of blasting holes, high drilling intensity, excessive crushing of stones, and serious over excavation, as shown in Fig.  2 . The number of boreholes for conventional tunnel drilling and blasting is estimated on the basis of the tunnel cross-section area S and the rock solidity coefficient f of \(N = 3.3 \cdot \sqrt[3]{{fS^{2} }}\) . The rock solidity coefficient f of the study section of the Gonghe Village Tunnel is 10, the tunnel section area S is 99.28 m 2 , and the number of blasting holes to be drilled in the whole section is 152, which is a huge drilling workload. The current tunnel rock drilling cart is expensive, has a high failure rate, and is limited by the tunnel space, which leads to the automated drilling technology not being mature and still mainly relying on manual drilling. Taking a 4 m depth of the blast hole as an example, the drilling efficiency of the workers is generally about 3 holes/h, and a drilling shift is calculated with 13 people, which takes about 3.9 h of drilling time per cycle, making drilling intense and long, and seriously affecting the construction progress. At the same time, the excessive number of blasting holes laid resulted in high usage of explosives, excessive damage to retained rock, and severe over excavation. The number of blasting holes, drilling time, explosives used, and average over-digging value per cycle of blasting in the upper bench of the study section of the Gonghe Village Tunnel were counted, as shown in Table  1 . Therefore, the traditional drilling and blasting method could not meet the requirements of safe and efficient construction of large cross-section tunnels, and there is an urgent need to put forward innovative theories and methods that can reduce the number of drilled holes, reduce the unit consumption of explosives, and ensure the quality of blasting.

Technical difficulties caused by the traditional drilling and blasting method

2.2 Theory and method of RHB

A typical compound wedge hollowing blast is used as an example to discuss the design method of traditional tunnel blasting parameters, as shown in Fig.  3 . In Fig.  3 , the orifice spacing, bottom spacing, row spacing, hollowing angle, and vertical depth of the first-order wedge-cut holes are S 1 , c , a , β 2 , and h , respectively. The orifice spacing, bottom spacing, row spacing, hollowing angle, and vertical depth of the second-order wedge-cut holes are S 2 , d , b , β 1 , and H , respectively. To determine the above blasting parameters, the following three steps are usually performed: (1) determine the bottom of hole spacing and row spacing based on the radius of the crushed zone and fractured zone, and further determine the orifice spacing based on the geometric relationship. (2) Determine the hollowing angle based on the force relationship of the slot cavity. (3) Determine the rest of the blasting parameters based on the geometry of the slot cavity volume by associating (1)(2).

Duplicate wedge hollowing blast analysis model

The destruction of rock in the slot cavity is based on the principle that the fractured zones of adjacent wedge-cut holes are interconnected, therefore, the row spacing of the wedge-cut holes a should be satisfied:

where R C and R T are the radius of the crushed zone and fractured zone, respectively.

When determining the spacing between the bottoms of the holes in the wedge-cut holes, the principle of overlapping fractured zones is used to ensure that the rock at the bottom of the slot cavity is sufficiently fractured. Therefore, the bottom spacing c and d of the wedge-cut holes should be satisfied:

Combined with the geometric relationship in Fig.  3 , it can be seen that the orifice spacing S 1 and S 2 of the wedge-cut holes should be satisfied:

The force state of the slot cavity lumen is further analyzed. When the wedge-cut hole charging section explosives explosion, the rock around the blasting hole in the strong compression of the explosive shock wave to form a crushed zone. Since the row spacing a of the wedge-cut holes is small, a through surface is formed in the charging section. Subsequently, the rock forms a fractured zone outside of the crushed zone under the combined effect of the blast stress wave and the blast-generated gas. Due to the presence of the hollowing angle, the explosion of the explosive generates a force perpendicular to the free surface outward, forcing the slot cavity to move in the direction normal to the free surface. As a result, the rock in the slot cavity will be damaged by shear with the surrounding rock, forming shear surfaces B 1 C 1 I 1 H 1 , A 1 D 1 J 1 G 1 , A 1 B 1 H 1 G 1 , and D 1 C 1 I 1 J 1 . The bottom of the slot cavity is subjected to large tensile stresses, forming damage surface H 1 I 1 J 1 G 1 .

The total resistance to blasting in the direction of the line of least resistance for the wedge-cut holes is:

where c and ε are rock cohesion and angle of internal friction, respectively. l c is the length of the charge.

The combined force acting on the explosive gas in the direction of the line of least resistance is:

where P is the average burst pressure in the blast hole, P  =  ρ 0 D 2 /8.

When the following conditions are met, the wedge-cut holes blasting is able to throw out the slot cavity smoothly and form a critical surface:

The value of the hollowing angle β 1 can be determined by associating Eqs. ( 6 )–( 8 ).

Ideally, the following relationship exists between the rock volumes V 1 and V 2 for first-order hollowing and second-order hollowing blasts:

From the geometrical relations in Fig.  3 , the values of the remaining parameters can be further determined:

After determining the parameters of the wedge-cut holes according to the above blasting parameter calculation method, the peripheral holes are laid out according to the requirements of contour molding, and finally the auxiliary holes are evenly arranged according to the size of the remaining section area and its location. The above blasting parameters determination method is more applicable to small cross-section tunnels, but with the increase of the tunnel excavation cross-section area, the above blasting parameters will lead to too many blasting holes.

Based on the demand for safe and efficient construction of large cross-section tunnel blasting, this paper proposes the theory and method of RHB for the blasting construction of the tunnel using a step method with more than three levels of surrounding rock, as shown in Figs.  4 and 5 . Central to this method are the extrapolation of wedge-cut holes, the addition of center holes, and the adjustment of the detonation sequence. The methodology is as follows:

The wedge-cut hole is pushed outward. The conventional drilling and blasting method places the wedge-cut holes in the lower middle of the tunnel excavation face, as shown in Fig.  4 a. The spacing of the wedge-cut holes is small, and a large number of auxiliary holes need to be laid to ensure the uniform distribution of the explosive energy, and the number of blasting holes is large. The RHB method pushes the placement of the wedge-cut holes outward to the maximum extent possible and to the minimum distance from the tunnel design contour line. This distance should ensure that blasting of the wedge-cut holes will not cause damage to the retained rock outside the tunnel design contour line, as shown in Fig.  4 b. At this time, the wedge-cut holes blasting forms a two-way critical surface (Lou et al. 2022 ): one provides a critical surface for auxiliary hole blasting; the other provides a critical surface for center holes blasting. From Fig.  4 , it can be seen that the wedge-cut holes are pushed out, which reduces the deployment of auxiliary holes in large quantities and reduces the drilling workload of the up-stage blasting excavation. To ensure the effectiveness of surface blasting, the two methods are consistent in terms of the placement of peripheral holes.

Addition of center holes. In this paper, the blasting holes laid in the center of the tunnel excavation face are defined as the center holes, which need to be loaded with explosives, and are able to break the larger volume of rock in the center of the excavation face by blasting through 2–3 center holes. As a result of the extrapolation of the wedge-cut holes, a large area of rock will be left in the center of the tunnel excavation face waiting to be blasted. After blasting the main wedge-cut holes, the rock in the center of the tunnel excavation face is "isolated" and forms three free surfaces simultaneously, so 2–3 center holes can be used to break this part of the rock. At this point, even if the charge of the center holes is increased, there will be no damage to the retained rock outside the design contour line of the tunnel, as shown in Fig.  4 b. In addition, the deployment of center holes can effectively solve the phenomenon of the "bulging belly" of the tunnel excavation face and improve the digging footage.

Adjustment of the detonation sequence. The traditional tunnel drilling and blasting method in terms of the detonation sequence is as follows: cut hole detonation, auxiliary hole detonation, peripheral hole detonation, bottom hole detonation. This paper optimizes the order of detonation adjustment. The adjusted detonation sequence is as follows: the main wedge-cut holes are detonated first, forming a large volume critical surface in the center of the working face, and providing a free surface for the secondary and tertiary wedge-cut holes, center holes, and collapse holes to be blasted. Then, the secondary wedge-cut holes and center holes are detonated at the same time, the secondary wedge-cut holes blasting for the tertiary level of wedge-cut holes and the collapse holes blasting to provide airspace. After a center hole is detonated, it is possible to fully break up the rock that has not been fully exploded at the bottom of the main wedge-cut holes, providing a larger critical surface. The tertiary wedge-cut holes and collapse holes are then detonated simultaneously to provide a critical surface for auxiliary hole blasting. Finally, the auxiliary holes, peripheral holes, and the bottom holes are detonated in turn, as shown in Fig.  5 .

Wedge-cut hole extrapolation theory and method

Adjustment of the detonation sequence

Compared with the traditional tunnel blasting construction process, the technical advantages of the theory and method proposed in this paper are mainly as follows: (1) the number of blasting holes and the drilling intensity have been reduced, and the construction efficiency has been improved; (2) reduction in the number of blasting holes, improvement in the phenomenon of wrong drilling and leakage, and improvement in the quality of blasting; (3) to curb the phenomenon of bulging belly, this method improves the digging footage to ensure the smoothness of the working face; (4) the order of detonation has been adjusted to change the sequence of energy release from the explosives, and the energy is utilized more efficiently; (5) reduced damage to retained rock outside the tunnel design contour.

2.3 Calculation of extrapolation distance for wedge-cut hole

Energy is an essential feature of the deformation response of rock and is the driving factor for the occurrence of destabilizing damage in rock (Xie et al. 2004 ), explosive blast rock is the result of the joint action of shock wave energy and explosive gas expansion energy (Zhao et al. 2019 ). After the explosion of the explosives, the energy consumed mainly consists of shock waves that expand the explosive cavity of the energy consumption W 1 , stress waves that produce radial fissures of the energy consumption W 2 , stress waves caused by elastic deformation of the energy consumption W 3 , bursting gas that expands the cavity of the energy consumption W 4 , and bursting gas that provides the energy consumption of the thrown rock debris W 5 . Several studies (Zhou and Zhong 2022 ; Leng 2020 ; Raina and Trivedi 2019 ) show that the energy utilization rate of explosive blast crushing rock is only 20–30% of the total release of chemical energy W 0 , and the vast majority of the remaining energy is consumed in other forms. Thus, this paper took 30% W 0 as the total energy of explosive blast crushing rock. The total energy consumed after the explosion of the explosive is W d , and when the residual energy W r (0.3 W 0 - W d ) is greater than the critical crushing energy dissipation density W a0 when the rock is damaged by impact loading, the rock will continue to be damaged.

Therefore, only W d and W a0 need to be determined to calculate the minimum distance of the wedge-cut holes from the tunnel design contour line. In Sect.  3.1 , the explosive energy dissipation law under the coupled action of in-situ stress and explosive loading is discussed, and the computational expression for the energy dissipation of each part under the action of the coupled stress field is proposed. As discussed in Sect.  3.2 , rock impact compression tests under different dynamic static combination loading conditions were designed to determine the critical crushing energy dissipation density W a0 of gray sandstone.

3 Parameter calculation

3.1 explosive energy dissipation law analysis, 3.1.1 calculation of the extent of the crushed and fractured zone under coupled stress field.

Before the tunnel is excavated, the surrounding rock is already in a three-dimensional stress state due to the self-gravitational stresses of the overlying rock. The in-situ stress has an inhibitory effect on the explosive load (Yan et al. 2015 ; Bastante et al. 2012 ; Hamdi et al. 2011 ; Mandal and Singh 2009 ), and the in-situ stress field of the original rock and the dynamic stress field formed after the detonation of explosives are superimposed onto each other to form a secondary coupled stress field. The expression for the stress distribution based on the coupled effect of blast load and in-situ stress is given by:

where r , r 0 are the distance from the calculation point to the center of the packet and the radius of the blast hole, respectively. θ is the angle between the line between any point in the rock and the center of the blast hole in the horizontal direction. P d is the homogeneous force acting on the borehole wall, MPa. α is the pressure attenuation coefficient, for the shock wave region α  ≈ 3 or α  = 2 +  μ /(1— μ ) and for the stress wave region β  = 2 −  μ /(1 −  μ ).

The expression for calculating the radius of the crushed zone R C when considering the effect of in-situ stress is:

where σ cd is the dynamic compressive strength of the rock mass, MPa. Let \(\frac{{r_{0} }}{{R_{C} }} = x\) , then Eq. ( 12 ) becomes:

Equation ( 13 ) can be solved using the MATLAB program, and excluding the limited understanding, the calculation expression of the crushed zone radius R C is obtained:

The expression for calculating the radius R T of the fracture zone when considering the effect of in-situ stress is (Ge 2020 ):

where σ td is the dynamic tensile strength of the rock mass, MPa. m is the coefficient of rock tensile strength enhancement caused by in-situ stress.

Further discussion on the enhancement factor m . The force state of the microelementary point under the action of coupled stress field is analyzed with reference to the research results of Ge ( 2020 ), as shown in Figs.  6 and 7 . According to Dai and Qian ( 2007 ), the initial static load on the rock mass actually increases the dynamic compressive or tensile strength of the rock mass indirectly. It is assumed that when the microelement point is compressed by a concentrated load ( σ V a ) in the vertical direction, the dynamic tensile strength of the rock in that direction is enhanced by 100%, i.e., the dynamic tensile strength in that direction becomes 2 σ td .

Force analysis of rock microelementary points under in-situ stress action ( λ is the lateral pressure coefficient)

Force analysis of rock microelementary points under explosive load

From the force analysis of the microelement points in Figs.  6 and 7 , it can be seen that the tensile stress on each microelement point is ( σa/λ ·sin θ 1  −  σa ·cos θ 1 ). Cracks are most likely to expand when the dynamic tensile strength of the rock is not enhanced, i.e., the crack length is longest when θ 1  = arctan λ . Taking the burial depth of 600 m as an example for analysis, when the lateral pressure coefficients λ are 0.2, 0.4, 0.6, 0.8, and 1.0, the longest cracks are in the directions of 79°, 68°, 59°, 51°, and 45° of the blasting hole, respectively. The values of the enhancement coefficient m in each direction of the borehole are shown in Table  2 , the variation rule of the enhancement coefficient m with θ under different lateral pressure coefficients λ is shown in Fig.  8 , and the variation rule of the enhancement coefficient m with the lateral pressure coefficient λ in the same direction of the blasting hole is shown in Fig.  9 .

Law of change of m with θ for different λ

Law of change of m with λ in the same direction of the blasting hole

3.1.2 Calculation of explosion energy under coupled stress field

After the explosive explodes, the rock around the blast hole in the shock wave produced by the violent compression decays, the hole wall continues to expand outward, and the blast cavity expands. The cavity expansion process ends when the shock wave propagates to the edge of the crushed zone. In the crushed zone, the energy dissipation of the shock wave is equal to the work W 1 performed by the shock wave in the process of cavity expansion:

where the explosion cavity radius \(R_{1} = \left[ {R_{C}^{2} - (R_{C}^{2} - r_{0}^{2} )\frac{{\rho_{m} }}{{\rho_{r} }}} \right]^{\frac{1}{2}}\) . r 1 is the blast cavity radius corresponding to r . ρ m is the original rock density, kg/m 3 . ρ r is the rock density behind the shock wave front at the blast hole wall, \(\rho_{r} = \frac{{(a + bV_{0} )\rho_{m} }}{{a + (b - 1)V_{0} }}\) , kg/m 3 . a and b are the rock test constants, and V 0 is the initial velocity of the rock particle at the blast hole wall. Let \(\frac{{r_{0} }}{{R_{1} }} = x_{1}\) , the calculation expression of shock wave expansion cavity energy dissipation W 1 can be obtained:

The shock wave expanding cavity consumes a large amount of energy and then decays into a stress wave, which has a stretching effect on the rock around the blast hole and forms a large number of radial fractures. The energy dissipation W 2 for the generation of radial cleavage by the stress wave can be expressed as (Zhang 2007 ):

where n is the number of radial fractures, generally taken as 10. K 1 is the stress intensity factor, \(K_{1}^{2} = \pi r\sigma_{\theta }^{2}\) . E m is the dynamic modulus of elasticity, GPa. Let \(\frac{{r_{0} }}{{R_{T} }} = x_{2}\) , the calculation expression of W 2 of the radial crack generated by stress wave can be obtained:

Outside the fractured zone, with the attenuation of the stress wave, the stress wave can only cause elastic deformation of the rock mass. At this time, the elastic deformation energy of the rock in unit volume is:

Let \(\frac{{r_{0} }}{{R_{E} }} = x_{3}\) , the calculation expression of elastic deformation energy dissipation W 3 caused by stress wave can be obtained as:

After the end of the shock wave effect, the explosion gas continues to act in the form of quasi-static pressure on the cavity wall, so that the explosion cavity continues to expand. The energy dissipation W 4 of the expression gas can be expressed as (Zhang 2007 ):

where R 2 is the final radius of the blast chamber, \(R_{2} = \left\{ {\begin{array}{*{20}l} {r_{0} \left( {\frac{{P_{0} }}{{\sigma_{cd} }}} \right)^{\frac{1}{6}} \begin{array}{*{20}c} {} \\ \end{array} \begin{array}{*{20}c} {} \\ \end{array} (\sigma_{cd} \ge P_{k} )} \hfill \\ {r_{0} \left( {\frac{{P_{0} }}{{P_{k} }}} \right)^{\frac{1}{6}} \left( {\frac{{P_{k} }}{{\sigma_{cd} }}} \right)^{\frac{3}{8}} \begin{array}{*{20}c} {} \\ \end{array} \begin{array}{*{20}c} {} \\ \end{array} (\sigma_{cd} < P_{k} )} \hfill \\ \end{array} } \right.\) . P 0 is the explosive gas pressure at the beginning of the expansion, P 0  =  ρ 0 D 2 /4, where ρ 0 is the density of the explosive, kg/m 3 , and D is the bursting speed of the explosive, m/s. P k is the critical pressure, MPa.

In addition to blast cavity expansion, the expression gas also throws the broken rock fragments due to the action of the blast stress wave. The energy dissipation W 5 of the expression gas throwing rock fragments can be expressed as (Zhang 2007 ):

where n 1 is the throwing action index of the blasting funnel, \(n_{1} = \frac{{r_{a} }}{W}\) , r a is the blasting funnel radius, and W is the minimum resistance line. For a standard blasting funnel, n 1 takes 1. \(V_{1} = \frac{{\sigma_{cd} }}{{0.38\rho_{m} C_{p} }}\) , C p is the longitudinal wave velocity. k is a constant related to explosives.

The total chemical energy released per unit length of explosive when it explodes is:

where Q is the explosion heat of the explosive, MJ/kg.

3.2 Critical crushing energy dissipation density of rock

The lithology of the surrounding rock in the study section of the Gonghe Village Tunnel is gray sandstone, and static and kinetic tests were carried out after on-site core drilling and sampling to determine the critical crushing energy dissipation values of the gray sandstone under different stress states. According to the specimen sizes recommended by the International Commission on Rock Dynamics (Zhou et al. 2012 ), the uniaxial compression test and triaxial compression test rock samples were machined as 50 mm × 100 mm cylinders, the Brazilian split test rock samples were machined as 50 mm × 50 mm cylinders, and the impact dynamics test rock samples were machined as 50 mm × 25 mm cylinders. The unevenness and non-perpendicularity of the rock samples were less than 0.02 mm, and the deviation of the end face normal was less than 0.25°. The rock samples are shown in Fig.  10 .

Rock samples

The static tests were carried out using a TAJW-2000 microcomputer-controlled electro-hydraulic servo triaxial rock test system as shown in Fig.  11 a, and the static parameters of the gray sandstone are shown in Table  3 . The impact dynamics tests were carried out on a detached Hopkinson lever test system, ALT100, as shown in Fig.  11 b.

The test systems used in this study

Based on the results of the static tests of the gray sandstone, the axial pressure ( σ V ) was set to 0, 10 MPa, 20 MPa, 30 MPa, and 40 MPa, which are 0%, 9.1%, 18.3%, 27.4%, and 36.6% of the static compressive strength, respectively, and the confining pressure ( σ H ) was set to 0, 4 MPa, 8 MPa, and 12 MPa.

The main purpose of this test is to determine the critical crushing energy density of gray sandstone under different dynamic and static combination loading conditions. Li et al. ( 2010 ) identified the state when the rock is broken into exactly 2–4 pieces as the critical damage state. At the beginning of the test, we set a certain air pressure to impact the rock sample, and if the rock sample is intact or only produces a small amount of cracks, we need to increase the impact air pressure. If a certain impact air pressure, the rock sample is broken into 2–4 pieces, this is the critical damage state. Continue to increase the impact air pressure, if the rock sample crushed, the previous impact air pressure is the critical impact air pressure. So we take the impact air pressure when the rock is exactly broken into 2–4 pieces as the critical impact air pressure, and we take the crushing energy density at this time as the critical crushing energy dissipation density.

During the test, to ensure the reliability of the test results, it is necessary to ensure that the stress on both ends of the rock samples reaches a state of dynamic equilibrium. The stresses, σ 1 and σ 2 , which are applied to the two ends of the rock sample can be calculated from the incident strain signal, \(\varepsilon_{I} \left( t \right)\) , the reflected strain signal, \(\varepsilon_{R} \left( t \right)\) , and the transmitted strain signal, \(\varepsilon_{T} \left( t \right)\) , according to the following equation:

Figure  12 shows the dynamic stress equilibrium curve of gray sandstone (with an axial pressure of 10 MPa, a confining pressure of 4 MPa, and an impact air pressure of 0.4 MPa). The combined stress curves of the incident and reflected waves are fundamentally consistent with the stress curves of the transmitted waves, indicating that the stresses at both ends of the rock samples are virtually in equilibrium during the test, which verifies the validity of the test process and the test results.

The dynamic stress balance curve

The critical crushing energy dissipation density of gray sandstone under the different dynamic and static combinations of loading conditions is shown in Table  4 . The curves of the critical crushing energy dissipation density of gray sandstone according to confining pressure and axial pressure are shown in Figs.  13 and 14 , respectively.

The variation curve of the critical crushing energy dissipation density according to confining pressure

The variation curve of the critical crushing energy dissipation density according to axial pressure

The maximum burial depth of the Gonghe Village Tunnel is about 1320 m. The rock density of the study section is 2.56 g cm −3 and the static Poisson's ratio is 0.37. Assuming that the lithology of the study section is homogeneous, the burial depths corresponding to axial pressures of 0 MPa, 10 MPa, 20 MPa, 30 MPa, and 40 MPa are 0 m, 391 m, 781 m, 1172 m, and 1563 m, respectively, when considering only the effect of gravitational stress. The dynamic Poisson's ratio of the lithology of the study section is 0.296, and the lateral pressure coefficient is 0.42, from which the corresponding confining pressures are 0 MPa, 4 MPa, 8 MPa, 12 MPa, and 16 MPa, respectively. Due to the equipment, the confining pressure of 16 MPa could not be loaded. Setting up the study conditions according to Table  4 can provide a basis for the design of blasting parameters for large cross-section tunnels under different stress states.

From Fig.  13 , it can be seen that the critical crushing energy dissipation density of gray sandstone increases with an increase in the confining pressure. The logarithmic function was used to fit the relationship between the changes; the fitting model and the fitting results are listed in Table  5 . It is evident that the confining pressure exerts a reinforcing effect on the gray sandstone samples; the greater the confining pressure, the more significant the reinforcing effect. The destruction of rock samples is a process of transition from a stable state to an unstable state under energy-driven action. Therefore, to destroy the gray sandstone samples, they must store more energy to reach their energy storage limit. Macroscopically speaking, this is manifested as the critical crushing energy dissipation density of the gray sandstone, which increases along with the increase in the confining pressure. As can be seen from Table  5 , the model’s fits at the axial pressures of 0 MPa and 20 MPa are relatively poor, which may be due to the discrete nature of the gray sandstone samples.

From Fig.  14 , it can be seen that the critical crushing energy dissipation density of the gray sandstone samples increases and then decreases with the increase in axial pressure. A quadratic function is used to fit the relationship between its changes, and the fitting model and fitting results are listed in Table  6 . From the previous analytical results, it is evident that axial pressure exerts a reinforcing effect on the gray sandstone samples when the axial pressure is small, while when the axial pressure continues to increase, the effect of the axial pressure on the gray sandstone samples is converted from a reinforcing to a deteriorating effect. Therefore, when the axial pressure is small, more energy needs to be absorbed to force the gray sandstone to destabilize. When the axial pressure continues to increase, the axial pressure has already caused internal damage within the gray sandstone; therefore, less energy needs to be absorbed in order to force the gray sandstone to destabilize.

From Table  6 , it can be calculated that the critical crushing energy dissipation density of gray sandstone reaches a maximum value of 7.01 J cm −3 when the axial pressure is 25.00 MPa, along with a peripheral pressure of 4 MPa. The critical crushing energy dissipation density of gray sandstone reaches a maximum value of 7.38 J cm −3 when the axial pressure is 28.33 MPa, along with a peripheral pressure of 8 MPa. The critical crushing energy dissipation density of gray sandstone reaches a maximum value of 8.40 J cm −3 when the axial pressure is 20.00 MPa, along with a peripheral pressure of 12 MPa.

3.3 Determination of extrapolation distance for wedge-cut hole

The main wedge-cut holes in the study section of the Gonghe Village Tunnel were loaded with a single charge of 3.0 kg in each hole and a charge length of 3.0 m. From Eq. ( 28 ), W 0 is calculated as 32.85 MJ, and the total chemical energy density is 32.85 J cm −3 , in which the heat of detonation Q of No. 2 rock emulsion explosives is taken as 4.5 MJ/kg. In this section, 30% W 0 is used as the total chemical energy released by the explosives when the main wedge-cut hole explodes, which is 9.86 J cm −3 .

The burial depth of the study section is 400 m, σ V  = 10.24 MPa, and σ H  = 4.3 MPa. The wedge-cut hole has a radius of 25 mm, a depth of 3.5 m, and a charge length of 3.0 m. The site uses No. 2 rock emulsion explosives, explosive density of 1.24 g cm −3 , and bursting speed of 4200 m s −1 . From the results of the study in Sect.  3.1 , it can be seen that the radius of the crushing zone R C is 58.28 mm, the radius of the fissure zone R T is 261.73 mm, the radius of the bursting cavity R 1 is 43.68 mm, and the final radius of the bursting cavity R 2 is 48.05 mm. W 1 , W 2 , W 4 , and W 5 were 1.98 MJ m −3 , 0.59 MJ m −3 , 0.14 MJ m −3 , and 2.08 MJ m −3 , respectively. At this point, the residual energy is 5.07 MJ m −3 . From the test results in Sect.  3.2 , the critical energy dissipation density of gray sandstone under this condition is 4.10 MJ m −3 . The residual energy is greater than the critical energy dissipation density and the rock mass will continue to be destroyed. Therefore, further consumption of explosive energy is required. Backcalculating the joint Eqs. ( 19 ), ( 21 ), ( 24 ), ( 26 ), and ( 27 ), the R E should be a minimum of 2.8 m when the residual energy is 4.10 MJ m −3 . It can be seen that for the upper bench blasting in the study section of the Gonghe Village Tunnel, the minimum distance of the main wedge-cut holes from the tunnel design contour line is 2.8 m. Compared with the conventional tunnel blasting method, the main wedge-cut holes of the RHB method were laid 1.4 m outward, as shown in Fig.  15 .

Schematic diagram of the extrapolation distance of the main wedge-cut holes of the RHB method

4 Parameter validation

4.1 model building.

ANSYS/LS-DYNA numerical simulation software was used to establish a three-dimensional numerical analysis model to compare and analyze the effect of hollowing out and the damage law of the retained rock body after blasting, so as to verify the reasonableness of the theoretical calculation results in Sect.  3.3 . For the main wedge-cut holes 2.4 m, 2.6 m, 2.8 m, 3.0 m, and 3.2 m from the tunnel design contour line, the overall dimensions of the model are 22 m × 18 m × 3.7 m (X × Y × Z), and the radius of the blasting holes and the radius of the pill rolls are 25 mm and 16 mm, respectively. The following simplifications are made to reduce the computational effort of the model: (1) only half of the overall model size is created when modeling, and after the model is calculated, the keyword *CONSTRAINED_GLOBAL is used to analyze the model after symmetry; (2) only primary wedge-cut holes, secondary wedge-cut holes, and center holes are modeled. The mesh size directly affects the accuracy of the simulation results. In this paper, we first refer to the research results of the literature to determine the preliminary grid size (Wang et al. 2016 ), and then comprehensively consider the calculation effect and calculation time, and finally select the rock grid size of 5 mm within the design contour line of the tunnel. The total number of modeled units is approximately 1.93 million. A simplified model is shown in Fig.  16 a, the grid division diagram is shown in Fig.  16 b.

Schematic of the simplified model and the grid division diagram

The in-situ stress σ V  = 10.24 MPa was applied to the upper and lower faces of the model, and the in-situ stress σ H  = 4.3 MPa was applied to the left and right faces (burial depth 400 m). The method of applying the in-situ stress is as follows: Define the load curve CURVE with the keyword *DEFINE, load from 0 to σ V (or σ H ), and use the keyword *INTERFACE to output the DYINA file with the ground stresses, replacing the original k file, to achieve the effect of applying the in-situ stress indicated in the model. The rock material is defined as a solid, the explosive and air material is defined as a fluid, the fluid is meshed in a co-nodal way, and the solid and the fluid are connected by fluid solid coupling. All faces except the free surface are set as non-reflective boundary conditions. The RHT model was used for the rock constitutive model, and the parameters of the RHT constitutive model are shown in Table  7 (Li et al. 2018a ; b ). The explosives, air, and gun clay material models were modeled using *MAT_HIGH_EXPLOSIVE_BURN, *MAT_NULL, and *MAT_SOIL_AND_FOAM material models, respectively, and the material models were taken with reference to the results of several studies in the literature (Liu et al. 2020 ; Wang 2020 ; Li et al. 2018a , b ). The blast parameters of the simplified model are shown in Table  8 .

4.2 Analysis of results

After the wedge-cut hole is extrapolated, whether the slot cavity can be successfully hollowed out is key to the success of blasting. The hollowing effect with different wedge shaped hollowing hole extrapolation distances is shown in Fig.  17 . Due to the clamping function of the rock, the rock in the slot cavity needs to overcome shear resistance and tensile resistance when being hollowed out. As can be seen from Fig.  17 , the hollowing effect gradually deteriorates as the wedge-shaped hollowing hole is extrapolated by an increasing distance. When the distance between the main wedge-cut hole and the design contour line of the tunnel is greater than or equal to 2.8 m, the explosive load can overcome the shear resistance and tensile resistance, and the rock in the slot cavity can be thrown out smoothly. At the same time, due to the role of center holes, the bottom of the hole will not show signs of the bulging belly phenomenon. When the distance between the main wedge-cut holes and the tunnel design contour line is less than 2.8 m, the spacing between the bottom of the wedge-cut holes is large, and the wedge-cut holes are able to form pre-cracking cracks after blasting, but are unable to overcome the tensile resistance of the rock at the bottom of the holes. Even if the center holes blasting can break part of the rock, it cannot also successfully hollow out the slot cavity, resulting in a serious bulging belly phenomenon, or even lead to blasting failure.

Effect of hollowing out

Damage to the retained rock outside the tunnel design contour after the wedge-cut holes have been extrapolated is another area of concern. The damage to the retained rock at different wedge-cut hole extrapolation distances is shown in Fig.  18 . As can be seen from Fig.  18 , when the distance of the main wedge-cut hole from the tunnel design contour line is greater than or equal to 2.8 m, blasting basically will not cause damage to the retained rock outside the tunnel design contour line. However, when the distance of the main wedge-cut hole from the tunnel design contour line is less than 2.8 m, blasting can cause extensive damage to the retained rock in the arch waist area. Peripheral hole blasting and post-blast drainage will result in more severe over excavation and affect the quality of blasting. Therefore, the optimum distance from the main wedge-cut hole to the tunnel design contour line in the study section of the Gonghe Village Tunnel is 2.8 m. The numerical simulation results are in agreement with the theoretical calculations.

Damage to retained rock

5 Field tests

Adopting the theory and method of RHB for large cross-section tunnel blasting proposed in this paper, five on-site blasting tests were carried out in the research section of the Gonghe Village Tunnel, and the plan view of the hole network design, the actual blast hole layout plan, the hole network design section plan, and the schematic diagram of the over-undercutting measurement point layout are shown in Fig.  19 a–d. In order to ensure the hollowing effect, the collapse holes were drilled at a downward inclination of 5°–10°, and the blasting parameters are shown in Table  9 . After the completion of blasting, the quality of blasting was comprehensively evaluated in terms of the excavation effect of the working face, the number of blasting holes, the drilling time, the utilization rate of the blasting holes, the unit consumption of explosives, and the over and under excavation.

Schematic diagram of aperture network design and monitoring point placement

Using the theory and method proposed in this paper for on-site blasting tests, the slot cavity can be successfully hollowed out, and the work surface is relatively flat, with basically no bulging belly phenomenon. After blasting was completed, the value of over undercut was measured at each measurement point, as shown in Fig.  20 . Data on the number of blasting holes, drilling time, utilization rate of blasting holes, unit consumption of explosives, and over and under excavation were collected, as shown in Table  10 .

Measurement of values for over and under excavation

As can be seen from Table  10 , by adopting the theory and method of RHB for large cross-section tunnel blasting proposed in this paper, the number of blasting holes per cycle of step blasting in the study section is reduced by an average of 21 holes, the drilling time is saved by an average of 0.5 h, the explosive unit consumption is reduced by an average of 0.16 kg cm −3 , and the value of over excavation is reduced by an average of 6.6 cm. The main reasons for the better contouring results of the RHB method compared to the conventional blasting method are as follows: (1) the wedge-cut hole pushed out to form a two-way critical surface after blasting, which can effectively block the stress wave during the center holes blasting and reduce the damage of the retained rock mass. (2) The number of auxiliary holes deployed was reduced, effectively minimizing the cumulative damage to the retained rock mass. (3) When the RHB method is applied in the field, the peripheral holes are loaded with axial spacing, and the explosive energy is distributed more evenly.

The cost of explosives on site is RMB 8.4 per kg, and the cost of the digital electronic detonator is RMB 16 each, whereas the research section of the upper step blasting can reduce the digital electronic detonator cost by RMB 320 per cycle while reducing explosives cost by RMB 302.4 per cycle. The total length of the right width of the Gonghe Village Tunnel is 10,698 m; by adopting the theory and method proposed in this paper, it is expected to save 1783 h of drilling time and about RMB 2.22 million on the cost of explosives. After the optimization of the program, the unit consumption of explosives is still high, which is due to the higher compressive strength (109.33 MPa) and better integrity of the rock in the study section, which requires more energy to be consumed to form crushed and fractured zones.

6 Conclusions

This paper put forward an RHB theory and method for large cross-section tunnels. The calculation method of explosion energy dissipation under the action of coupled stress field is given, the critical energy dissipation density of rock under different stress states is determined, and the calculation method of the extrapolation distance of wedge-cut holes is constructed.

The critical crushing energy dissipation density of gray sandstone increases with the increase in peripheral pressure, and the change rule conforms to the logarithmic function relationship. The critical crushing energy dissipation density of the gray sandstone samples increases and then decreases with the increase in axial pressure, and the change rule conforms to the quadratic function relationship. The critical crushing energy dissipation density of the gray sandstone samples under the conditions of confining pressure of 4 MPa axial pressure of 25.00 MPa, confining pressure of 8 MPa axial pressure of 28.33 MPa, and confining pressure of 12 MPa axial pressure of 20.00 MPa reached maximum values of 7.01 J cm −3 , 7.38 J cm −3 , and 8.40 J cm −3 , respectively.

The optimum distance of the main wedge-cut holes in the study section of the Gonghe Village Tunnel from the tunnel design contour is 2.8 m. The number of drill holes per cycle of step blasting in the section used in this study was reduced by about 15.8%, the drilling time was reduced by an average of 0.5 h, the unit consumption of explosives was reduced by an average of 0.16 kg cm −3 , the value of over excavation was reduced by an average of 6.6 cm, and the cost of explosives was reduced by an average of RMB 622.4.

Availability of data and materials

Data will be made available on request.

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This study was supported by the National Natural Science Foundation of China (52064008) and Guizhou Province High-level Innovative Talent Project (Qianke He Platform Talent-GCC [2022] 004-1).

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Xingchao Tian: proposing of the theory and methodology, designing of experimental plan, analysising of experimental data, writing original draft. Tiejun Tao: Editing and checking of manuscript. Caijin Xie: uniaxial compression test, triaxial compression test, brazilian splitting test, and dynamic shock compression test.

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Tian, X., Tao, T. & Xie, C. Research on the theory and method of reduced-hole blasting for large cross-section tunnel based on explosive energy dissipation. Geomech. Geophys. Geo-energ. Geo-resour. 10 , 96 (2024). https://doi.org/10.1007/s40948-024-00816-3

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Received : 24 January 2024

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DOI : https://doi.org/10.1007/s40948-024-00816-3

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