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Peer-Review Record

Failure Behaviour of Jointed Rock Masses with 3D Nonpenetrating Joints under Uniaxial Compression: Insights from Discrete Element Method Modelling

Appl. Sci. 2022, 12(21), 11027; https://doi.org/10.3390/app122111027

by Rihong Cao^1,2,3, Hua Dai¹

, Rubing Yao^1,*, Hang Lin^1,*

and Kaihui Li¹

Reviewer 1:

Siwei Meng

Reviewer 2:

Marcin Graba

Appl. Sci. 2022, 12(21), 11027; https://doi.org/10.3390/app122111027

Submission received: 12 October 2022 / Revised: 26 October 2022 / Accepted: 28 October 2022 / Published: 31 October 2022

(This article belongs to the Special Issue Advances in Failure Behavior of Rocks)

Round 1

Reviewer 1 Report

In this study, a series of numerical simulations were performed to explore the uniaxial compressive strength and failure mechanisms of 3D nonpersistent joints with different inclinations and persistence. In addition, the failure mode and stress evolution in the loading process were analyzed.

1. What is the rock type in this paper, and why do you choose the joint type in this paper?

2. The size of 70×70×140 was selected for the model, and why the model is not in accordance with the standard recommended by ISRM.

3. what are the mechanics parameters of Tables 1 and 2 based on. It is recommended that the authors calibrate the parameters.

4. The peak intensity is conventionally recognized as the lowest at 90° inclination, while this paper is the lowest at 60° inclination, can the author please explain why?

5. Figure 7 presents the comparison of the damage mode with the experiment, what does not have the comparison of the stress-strain curve, it is suggested that the authors give the comparison of the stress-strain curve.

6. The curve in Figure 13 called failure patterns is not very reasonable. In addition, why is the shear crack percentage at strain 0 is 1, meaning complete shear damage when no load? Suggest the author to reconsider the expression of this figure.

7. Figures 15 and 16 should mark the corresponding strain points.

Comments for author File: Comments.pdf

Author Response

For reviewer #1:

Comment #1: What is the rock type in this paper, and why do you choose the joint type in this paper?

Response: Thank you for your valuable comments. The rock type is a rock-like specimen made from cement mortar. The distribution and shape of joints in natural rock is random and it is difficult to achieve control of internal joint conditions (dip or penetration, etc.) using real rock, so the damage characteristics under different joint conditions (dip or penetration) are investigated using a cement mortar-like specimen. The section is made with a partially penetrated joint sheet, which is chosen to enable control of jointed rock bridges, and the stress evolution over a single joint type is well investigated for damage damage to the specimen.

Comment #2: The size of 70 70 140 was selected for the model, and why the model is not in accordance with the standard recommended by ISRM.

Response: Thank you for your valuable comments. When using the specimen size recommended by ISRM, the area of the generated joint area is smaller the area of the rock bridge on the joint surface is also smaller, which makes it difficult to achieve control of different degrees of penetration. Using a larger specimen size makes it easier to control the area of the bridge when making a specimen so that different degrees of penetration can be achieved.

Comment #3: What are the mechanics parameters of Tables 1 and 2 based on. It is recommended that the authors calibrate the parameters.

Response: Thank you for your valuable comments. Experimental results and simulation results (Table 1.) have been newly added in the article as a basis for parameter calibration.

Comment #4: The peak intensity is conventionally recognized as the lowest at 90° inclination, while this paper is the lowest at 60° inclination, can the author please explain why?

Response: Thank you for your valuable comments. In general, the strength of a rock mass is influenced by the direction of loading and the angle between the structural faces; for a single structural face, when the main stress is parallel to the structural face, the rock mass is damaged by lateral extension in tension at the structural face, but this does not mean that the strength of the rock mass is close to the tensile strength of the structural face; in fact, after the structural face of the rock mass is damaged, the rock mass still has a strong axial bearing capacity and its strength and damage mode are similar to that of an intact rock mass (which This is also consistent with the experimental results of the article); therefore, the rock strength is not the lowest for a single structural face at 90° dip; in this study, the specimen undergoes complete shear failure at 60° and the rock undergoes significant slip damage along the single structural face, and the shear action of the rock along the structural face makes its strength the lowest and close to the structural face strength.

Comment #5: Figure 7 presents the comparison of the damage mode with the experiment, what does not have the comparison of the stress-strain curve, it is suggested that the authors give the comparison of the stress-strain curve.

Response: Thank you for your valuable comments. The results of the experimental and simulated curve comparisons have been given in the article (Figure 8).

Comment #6: The curve in Figure 13 called failure patterns is not very reasonable. In addition, why is the shear crack percentage at strain 0 is 1, meaning complete shear damage when no load? Suggest the author to reconsider the expression of this figure.

Response: Thank you for your valuable comments. The name of Figure 13 has been revised. Figure 13 represents the evolution of the crack percentage during uniaxial pressurisation. When the pressurisation begins (strain 0), microcrack generation is initially shear cracking, so the crack percentage is 1. As the loading continues, new tensile cracks appear and the shear crack percentage continues to decrease.

Comment #7: Figures 15 and 16 should mark the corresponding strain points.

Response: Thank you for your valuable comments. It has been revised in the article.

Author Response File: Author Response.docx

Reviewer 2 Report

There will be many abbreviations, markings and symbols in the paper. Not all of them are explained - and they should be. Thus, it should be done in the text of the paper, as well as authors should introduce nomenclature. It is necessary.

The words "work, works" should not be used in relation to scientific articles - the preferred forms are "paper, manuscript, scientific article".

The test material should be described with the word "specimen", not "sample".

The authors of the manuscript do not respect the correctness of notation of quantities with indexes. It needs to be standardized. An example is formula (1) and the comment on line 125 of manuscript - it is inconsistent. If a quantity in a formula appears with an index, then it should also be used as such, and not without considering the entry in the form of an index.

Please attach a technical drawing of the specimen to the manuscript, along with all dimensions.

Table 2 - There is no "Gpa" unit - the unit is "GPa". Please correct it. Also, to avoid ambiguity in the notation, please change the unit from the form "(?p? ?⁻¹)" to the form "(?P?×?⁻¹)".

Authors should check the text of the manuscript very carefully, especially tables and figures. There should be a space between the comment to the quantity (somehow denoted by the symbol) and the description of this quantity and the unit. There cannot be "/" or "\". Exemplary correct notation - " Yield stress, s, (MPa)" or " Yield stress, s [MPa]". An example of an error is Table 2 or Figure 4.

All graphs and figures need to be standardized, they have to be developed in essentially the same way. Axis descriptions should be made in the same font - the font size must be the same. This also applies to the legend in the diagrams, they also need to be unified, as well as additional comment in the figures.

I do not recommend dividing figures between pages.

I also recommend a linguistic proofreading of the paer. A professional editor must check it.

The manuscript is worth attention. However, some corrections and additions need to be made. I suggest major revision and refer the paper for re-review.

Author Response

For reviewer #2:

Comment #1: There will be many abbreviations, markings and symbols in the paper. Not all of them are explained - and they should be. Thus, it should be done in the text of the paper, as well as authors should introduce nomenclature. It is necessary.