Geotechnical Investigations and Support Design for an Underground Powerhouse of Pumped-Storage Power Station: A Case Study in Chongqing, China
Round 1
Reviewer 1 Report
The Authors have presented a manuscript on the use of distinct element code to model a rock mass within which an excavation would be constructed for housing a powerhouse. Subsequently, the numerical model was used to assess the extent of the plastic zone within the rock mass, as well as the distribution of stresses on the reinforcements (i.e. anchor bolts). There are a number of technical issues with the manuscript, as detailed in the comments, hereinafter. These technical issues are significant, as there are inconsistencies (e.g. the reporting of Mohr-Coulomb parameters, the identification of significant jointing, and finally the use of Hoek-Brown rock mass parameters). These could result in significantly different findings. The presented grammar requires significant improvement. Based on these issues, this Reviewer recommends for the manuscript to undergo MAJOR REVISION.
Please clarify what is meant by "flow direction" in the stereo nets.
It is unclear why interpretation of the experimental results in Fig. 5 were based on Mohr-Coulomb (MC) failure criterion. This is not appropriate, especially when more suitable constitutive models (such as Hoek-Brown) are more effective at modelling rock masses.
The purpose of the rock mass classifications is unclear. How is this information used in the distinct element model?
According to Table 2, the joints have been described as "wet" under Q system and HC method. There is also mud infill for the mudstone under HC method, with the mudstone being classified as Grade V. For this mudstone, please justify the use of rock mass properties in the numerical model without considering rock joints / discontinuities.
Even though the rock layers are numbered 1 to 5, the properties of each layer are unclear. Table 4 only presents there sets of rock mass properties.
Please change the naming of the zones in Fig 7. It is easy to confuse this with the rock type (rock weathering grade), since both the zones and the rock types are using Roman numerals.
The boundaries should be far enough from the tunnel such that the modelling results (plastic zone, anchor stresses, etc.) are not influenced by the boundaries. Furthermore, Fig. 2 indicates that the the powerhouse is significantly deeper than the height of the model. This implies that the numerical model will neglect the effects of confinement pressure, thus wrongly estimating the plastic zone.
In Fig. 9, for the bottom row of figures, please present a legible legend for the different colours.
In Fig. 9, the distributions appear symmetrical. The structural geology (direction of joints) does not seem to be reflected in the results. Please clarify.
In Fig. 10, the excavation geometry does not appear to be the same as that from the other results presented in Fig. 9 and Fig. 11. Please clarify / amend as necessary.
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Reviewer 2 Report
In this paper, the authors firstly investigated the geology conditions of an underground powerhouse, then performed numerical simulation using 3DEC. A lot of experiments have been conducted and the results of the numerical simulation seem to be reasonable. However, the manuscript is not good enough to be published as an academic paper. Firstly, the research topic is unclear and scientific problems should be refined concisely. Why do the authors conduct this study? Are there any difficult engineering problems the authors meet? What are they? This should be clarified in the Introduction Section. Secondly, another problem exists in the weak links between different parts of the paper. For example, are all parameters in Table 2 used for numerical simulations? How to determine the rock properties used in the numerical model from the geology investigation? Finally, it is strongly suggested that written English should be improved sufficiently. Other problems are listed in detail.
1. Font size in Figures should be larger. For example, the tick labels in Figure 2 are too small.
2. The physical and mechanical properties of intact rocks are listed in Table 1. How many samples are tested in each experiment group? What is the variance of the experimental result? What are the “Group 1” and “Sheet1 D” in Figure 5?
3. There are many equations in this paper. How to determine the values of some parameters in these equations? For example, why is the value of ω in equation 1 0.785? Since the blast issues are not discussed in this paper, how to determine the “D” in equation 2? By the way, is the “D” in equations 2 and 8, and the “D” in Table 2 the same “D”? Maybe, a symbol list should be added at the beginning of the main text.
4. A more detailed description of the numerical modeling is strongly suggested, especially the meshing.
5. Any comparison between numerical and field monitoring results? Why do the authors conduct the numerical simulation?
6. An in-depth discussion of the experimental and numerical results is strongly suggested to improve the quality of this research.
Author Response
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Reviewer 3 Report
In this manuscript, based on the main workshop of Panlong Pumped-storage power Station, the geomechanical properties and rock mass classification of the complete rock and rock mass are evaluated through field geological survey and laboratory test. Then, the supporting parameters and excavation method of underground structure are designed empirically, and the supporting effect is analyzed by 3DEC numerical method. In general, the logic of the manuscript is not clear enough, the innovation is not fully reflected, and the argumentation of many issues is not unclear. The manuscript appears to be an experimental report. Some issues need to be well addressed, as shown below:
(1) The manuscript has a lot of language problems. It must be carefully checked and perfected.
(2) Line 32-88:The main purpose of the introduction is to fully review the existing research results and explain the inadequacy of existing research to explain the significance of this study. This goal is not achieved in the current manuscript, so it is suggested to improve the introduction again. This sentence ("However, rock classification methods do not provide the plastic zone thickness and stress distribution around excavation opening zone.") is not enough to support the innovation of this paper.
(3) Line 64-81: This is the background of the project and should not be covered in the introduction. It is recommended to move to section 2.
(4) Line 120-121: Please add the legend in Figure 2.
(5) Line 165: The content shown in Fig. 5 is undoubtedly a meaningful reference for the numerical modeling in section 4 of the manuscript. In addition, it seems that section 3 of the manuscript has not been applied to this test result. Could you adjust the content to Section 4? This is good for the integrity and logic of the manuscript.
(6) Line 231-325: This section describes four types of rock mass classification systems, and gives the relative results of rock mass classification. Why are only HC systems used in support and excavation scheme determination? Please explain the significance of analyzing the four rock classification systems.
(7) Line 327-339: Fig. 2 shows that there are various strata in the surrounding rock of the cavern. How is this considered in numerical models? How to consider the way of block partition in the model? How to deal with the contact between support and surrounding rock? How to realize model excavation sequence? The correctness of these methods will directly affect the reliability of numerical simulation results. The modeling process and details need to be explained.
(8) Line 328-372: How are rock mass parameters and joint parameters used? How to value support (bolt, etc.) parameters? Please explain in detail.
(9) Line 373: Besides the displacement and plasticity of surrounding rock, the variation of surrounding rock stress distribution is the cause of the former. Why not do an analysis? The analysis system of numerical simulation results should be strengthened.
Author Response
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Reviewer 4 Report
This paper talks about "Geotechnical Investigations and Support Design for An Underground Powerhouse of Pumped-Storage Power Station as a case study in China. The authors used 3DEC for their numerical investigations. I am generally fine with this paper, however, I have the below questions from the authors; and the paper may be published after their revisions:
1- I am wondering why the references in the body of the paper sometimes cited as XXXX (year) and other times like (XXXX Year). Please be consistent for all.
2. Fig.2's quality is really bad and needs to be replaced by a higher quality one. I also do not see much explanation in connection to this Fig.
3. In Fig. 4, I see the numbers; But I strongly encourage the authors to make the numbers larger for a better readability.
4. In Fig.5, I see the equations but the plots are messy and the equations cannot be identified. Please revise this fig. as well.
5. The english needs to be revised by a native english speaker. I do see several grammar errors.
Author Response
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Round 2
Reviewer 1 Report
The Authors have addressed the earlier review comments, and the manuscript has been substantially improved. The inclusion of field measured results allows for validation of the numerical model. A few minor typographical errors still remain. There is still the remaining issue of using Mohr-Coulomb (MC) failure criterion, especially when the test results demonstrate nonlinearity. Therefore, this reviewer recommends for the current manuscript to undergo MINOR REVISION.
Line 163: Should be "in-situ" instead of "in-suit".
Lines 165-166: Is this referring to the structural plane between mudstone and sandstone? Please correct.
Lines 166-167, Fig. 5b: The results clearly show nonlinearity. Using a linear 'best fit' does not address this nonlinearity, and could result in under- or over-estimation of MC parameters. Therefore, the MC failure criterion is not appropriate. Suggest to use a nonlinear stress-dependent constitutive model, and apply it to all subsequent analyses.
Lines 167-169: Please look into the sentence structures here. "... much attention should be paid to this area" is a general statement. Suggest to omit this.
Lines 169-170: What do you mean by "other support methods should be stalled to ensure stability"? Is there an error here?
Lines 178: Please reference the standard(s).
Line 318: Should be "The Chinese standard gives a..."
Lines 318-319: Please reference the standard(s).
Lines 354-355, Fig 8: It is helpful to use sub-captions to inform the readers on the different parts of the figure.
Line 388: Missing symbol in the equation.
Author Response
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Reviewer 2 Report
The authors have revised the manuscript carefully, and it will be acceptable after moderate changes of English. English language and style are expected to be enhanced. The authors may ask native English speakers for help.
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Reviewer 3 Report
In the new manuscript, the level of research has improved significantly. My concerns were answered reasonably by the author. But there is still a problem that the author needs to consider fully:
Combined with the supporting parameters given in the manuscript (bolt diameter 32mm), the axial force of bolt in FIG. 14 far exceeds the bearing capacity of ordinary bolt. The exceeding value is 5~10 times of the limit value of ordinary bolt. Obviously, there are huge errors between numerical simulation results and engineering practice. Are the numerical simulation results reliable?
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Reviewer 4 Report
This version of the paper can now be published in its current form.
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