Experimental Study on the Effect of Single Structural Plane on the Stability of Shallow Tunnel Surrounding Rock
Round 1
Reviewer 1 Report
In this paper, the author studies the impact of a single structure plane with different inclination angles on the tunnel by constructing a small tunnel physical model, and conducts a simulation study, which has a certain research significance. However, there are some errors in the paper that need to be corrected. I suggest that it is acceptable with minor modifications. The modification suggestions are as follows.
1. How is the model material selected for the test？
2. How is the similarity ratio of the model considered? Please explain.
3. What types of crack propagation are corresponding to different dip angles? It is suggested to classify the types of crack propagation.
4. In Figure 4, when the dip angle is 60 °, what is the reason for no post-peak strength?
5. In Figure 6, the crack propagation type is the most complex when the dip angle is 45 ° and 60 °, and it is recommended to make relevant explanation.
6. Is there a relationship between the direction of the maximum principal stress and the direction of inclination? What's the impact?
7. Please perfect the introduction and conclusions.
Author Response
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Reviewer 2 Report
Investigations of the effect of a single structure on the deformation and failure mode of the rock mass surrounding the shallow tunnel are discussed. Based on extensive laboratory testing of samples that included a tunnel chamber and interfaces oriented at different dip angles, convincingly substantiated conclusions were made. Of great utility, in my opinion, are the distinguished types of failure mode of the rocks surrounding the tunnel and the method of predicting the strength of the rock mass characterized by a larger number of interfaces.
Laboratory tests used artificially manufactured rock material and artificial interface molds for good reasons. However, it is unfortunate that the Authors did not provide their view of the extent to which the research results they described in the article can be implemented in engineering practice.
Detailed remark:
Lines 416 and 417 - angles q1 and q2 are not marked in Figure 15. Can you please complete?
Author Response
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Reviewer 3 Report
After carefully examining the manuscript "Experimental study on the effect of single structrual plane on the stability of shallow tunnel surrounding rock", I reckon that it needs minor improvement to be considered for publication on the Applied Sciences.
The main points that need to be clarified by extended critical discussion and interpretation are:
- does uniaxial compression carried out in the lab correspond, even qualitatively, to the stress field to which a structrual plane crossing tunnel is subjected? If so, is this valid for every situation or just for some particular situations?
Some other considerations are listed in the following.
In the introduction, I suggest to add considerations and references about other works available in the literature focused on the physical modelling of influence on surrounding rock of structural plane .
In materials and methods:
- improve figure description
- add considerations about representativeness of the model compared to the real case
- what is the meaning of wave velocity measurement in the model which is heterogeneous? In which direction do the wave travel?
In results:
-figure 7 need to be improved, the annotations are difficult to recognize
-what is the relationship between the fracture development pattern in figure 8 and real tunnel?
In discussion:
- what is the basis of material parameter ?
- what’s mean of ‘S’ shaped track lines ? Please note in figure
- can you explain the physical significance of formula 11
Conclusions should be extended by highlighting how the reported results can be applied to other situations and for which aspects the tested model can/cannot be considered representative of reality.
Author Response
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Reviewer 4 Report
In the manuscript, the authors implemented uniaxial compression experiments on a tunnel model with interfaces that have different inclination angles. Analytical and numerical simulations were deployed to understand the failure mode of the tunnel structure. The idea of designing the experiments is of great interest. However, some issues should be addressed before acceptance for publication. One problem is the lack of sufficient explanation for all figures in each caption. Other comments are given below:
1. The abstract is not clearly informative of the gist of the manuscript. Suggestion of rewriting part of the abstract (Line 17 - 21) should be taken.
2. In the introduction, many references were cited to discuss tunnel stability with specific deformation mechanisms, and empirical strength models for rocks with discontinuities. However, it is not clear about the motivation of the current work from literature. It is suggested that the authors clearly state why doing the experiments and numerical modeling, based on the existing literature works.
3. What are the “other types of interfaces” in Line 76? You should clearly define those terms for clarity of reading.
4. Figure 1 and 2 were shown here without any explanations. Can you label tunnel span and thickness of cover soil in Figure 2?
5. The figures in Table 1 are with round holes, which is different with the actual configuration. Error bars should be given in Table 1 to test the repeatability of wavespeed measurements.
6. Can you comment on the size effect on the uniaxial compressive strength from your experiments?
7. What are the definitions of a and \phi in Line 176
8. It should be figure 6 in Line 183. And what are the displacements when Figure 6 being captured. The x and y label values of this figure are not discernable.
9. Different types of fracture were mentioned in Line 246 – 250. It is not clear what are those cracks in Figure 7, which should be clearly labeled for separation. Different colors can be used for labeling on Figure 7, as a suggestion.
10. How did you extrapolate the 3D fracture configuration figure 8 from a 2D surface visualization? What if the crack propagates differently along the thickness? Do you have the volume measurement, such as microCT to confirm this extrapolation from 2D to 3D?
11. It is worth comparing the uniaxial compression tests with real tunnel interface structure to validate experimental design.
12. What does the “o” symbol mean in each subfigure in Figure 9?
13. What is the meaning of \alpha in equation (1) and Lin3 344, and what is the motivation of doing those calculations? The application of \alpha values should be given explicitly.
14. If you decompose the problem in to two parts as shown in Figure 11, how could you meet the free boundary condition around the tunnel surface?
15. What’s the definition of a and b in equation (3) and (7), and why those values in Table 2 are absent for inclination angle below 60 degree? How were the a and b values obtained? What is the definition of \beta in equation (8)? The intermediate steps for the derivation of equation (4) and (5) should be given for a better understanding of the equations.
16. Did you plot the dashed curve using equation (6)? Equation (6) is a piecewise continuous function; however, the dashed curve is a smooth curve which does not show features of discontinuity.
17. Figure 15 can be very misleading. Apparently, the upper left block and lower right block cannot reach force equilibrium from the diagram, which need to be addressed.
18. Symbol \mu has been used as the Poisson’s ratio in equation (2), and it cannot be reused as friction coefficient in equation (9) and (10).
19. What is the motivation or physical background of using a linear fit function to express stress relations in equation (11)? The dependence of combined strength with the two strengths of rock mass is not clear.
Author Response
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