A new loading–unloading experimental method for simulating the change of mining-induced stress

Based on a self-developed triaxial seepage device, a new loading and unloading experimental method is proposed in this paper to eliminate sample variations. The results show that the strength of sandstone sample and the axial strain at failure increased with the increasing initial hydrostatic stress, but decreased with the increasing loading–unloading rate. Following the alternating loading–unloading test, the stress–strain curves of specimens advanced in wave form, the waves' volatility decreased and then increased. It is found that near the ultimate strength, volatility is the biggest, and the stability of waves’ volatility increased along with the increasing initial hydrostatic stress. The similarity of stress–strain curves between the conventional loading–unloading tests and the alternating loading–unloading tests increased along with the increasing initial hydrostatic stress and the increasing initial velocity for the alternating loading–unloading method. Along with the increasing initial hydrostatic stress, the failure behaviour of the sandstone samples tested under loading–unloading methods changed from a tensile state to a tensile-shear coexisting state, and finally to a fully shear failure state. The degree of failure modes increased with the increasing loading–unloading rate.


08-Apr-2019
Dear Professor Jiang On behalf of the Editors, I am pleased to inform you that your Manuscript RSOS-181964 entitled "A new loading-unloading experimental method for simulating the change of mining-induced stress" has been accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the referees' comments at the end of this email.
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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch. Comments to the Author(s) The manuscript carried out alternating loading and unloading experiments under different confining pressures and different loading-unloading speeds, alternating the rate of loadingunloading on the sandstone sample. A new experimental method for obtaining different experimental curves of loading-unloading speed on the one sample was creatively studied in the manuscript, and the feasibility of the new method was verified. The experimental method has certain innovation and practicality, and provides a new idea to eliminate sample dispersion. However, there are still some things that need minor improvements. 1. It is recommended to provide more detailed information or physical parameters (such as location, density.) of the sample so that other researchers can judge and understand the work of the paper.
2. It is best to explain in detail the meaning of △σ on the 21st line of page 4, and the meanings of the lower right corner of Figure 3 and Figure 4 (such as 6(0.1), 6(0.01).). 3. English should be checked again, there are some spelling mistakes in the paper, such as the semicolon in the abstract, the words after the comma should be lowercase, I suggest a native English speaker check it English before re-submission.

Reviewer: 2
Comments to the Author(s) I wrote some suggestions to authors of this article (in attachment)

21-May-2019
Dear Professor Jiang, I am pleased to inform you that your manuscript entitled "A new loading-unloading experimental method for simulating the change of mining-induced stress" is now accepted for publication in Royal Society Open Science.
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Comments:
1. The article may be interesting from the point of view of mining and also during any construction works requiring e.g. tunnel drilling. Considering the practical aspect of the research, reading the article, I noticed the lack: -Direct reference to mining. The part of the title of the article is "simulating the change of mining-induced stress". The authors focused on presenting the result of the experiment, but without presenting what these research actually bring to mining practice. Do they have any practical applications? If so, it has not been clearly articulated. The title suggests that the work is related to mining, but it does not really follow from the content. -I did not see a clear purpose of research. If the authors consider the text from page 3 19-21 as a purpose of research ("Through the method of the test, the mechanical of characteristics of characteristics loading characteristics loading-unloading rates were more accurately, and the theoretical guidance of rock excavation was more scientifically"), they maybe should make reconstruction of the title or also purpose of research. The contents of the article suggest more theoretical and laboratory practical considerations rather than the impact on mining...
2. I understand that the authors of the article for the purpose of the research use a device constructed for the analysis of coal containing methane (Triaxial servo-controlled seepage equipment for thermo-hydro-mechanical coupling of coal containing methane). The article in which they describe the device (In references No. 29 -It was printed in the Chinese magazine) is not generally available, so I suggest to include even a brief description of the device (this is self-made so this is interesting for readers). If this device was made for coal research, why you decided to apply it to sandstone samples?
3. Sampling -why was this rock chosen? Is a device made for coal suitable for a different rock? The name has clearly to "coal". Do the authors know the characteristics of the analysed sandstone. Can you assume this sandstone is fairly homogeneous, as isotropic? Because it ensures the repeatability of the measurement. The authors write (p.3, 57-58) about "without visible fractures and cracks by means of photo observation". Which means "photo observation"? Did you watch it under any microscopic magnification? Did you use any microor only macro analysis ? Were any petrographic analyses carried out? Is composition is known (skeleton, matrix, cement)? Do you know any physical properties of these rocks?
4. The article contains a fairly wide references review, but it focuses on samples other than sandstones -the authors write about mechanical properties: coal, marble salt rocks, granite, migmatite, and even man-made rocks (similar as sandstones but more homogeneous) e.t.c. But the part about the behaviour of sandstones and research on them is relatively poorly developed. Sandstones are, after all, very common rocks, especially as rocks accompanying in mines. Sandstone research has been and is being carried out on a large scale, which is why I think it is worth reaching deeper into the literature on the mechanical properties of sandstone.
There are a number of works dealing with clastic rocks in the context of strength.

Conclusion:
The article can be printed, but I suggest a deeper analysis of the sandstone references, maybe rewording the title or purpose of the research, as well as a brief description of the device and method, Appendix A explaining why this device was applied to the sandstone. And in the future, a little more emphasis on the physical and petrographic properties of used samples.

Response to Editor and Reviewers
Dear Editor and Reviewers, We deeply appreciate the critical comments concerning our manuscript. These comments are very valuable and helpful for improving our paper. We have studied all the comments carefully and have made corrections accordingly.
The main corrections in the paper and the responses to the reviewers' comments are given as follows.
Revisions in the text are shown using red highlight for additions, and blue highlight for grammatical checks. We hope that the revisions in the manuscript and our accompanying responses will be sufficient to make our manuscript suitable for publication in Royal Society Open Science.
We deeply appreciate your critical comments concerning our manuscript. The manuscript has been resubmitted to the journal and we look forward to your positive response at your earliest convenience. pressure is 9 MPa, the axial compression is changed. The loading-unloading speed is 0.1 MPa/s, and the loading-unloading speed is 0.01 MPa/s when the shaft is pressed to 12 MPa, and goes on with this change until it breaks down. 6 (0.1→0.01) in Fig. 4 indicates the stress-strain curve of the sample No. 2-6-2 in the experimental scheme 2, wherein 6 indicates that the initial hydrostatic pressure is 6 MPa, and (0.1→0.01) indicates that the initial loading-unloading speed is 0.1 MPa/s, the conversion loading-unloading speed is the time when the axial stress increases by 3MPa. For example, when the axial pressure is the initial hydrostatic pressure of 6MPa, the loading-unloading speed is 0.1 MPa/s, and when the axial pressure is 9MPa, the transformation loading-unloading speed is 0.01 MPa/s, when the axial pressure is 12 MPa, the transformation loading-unloading speed is 0.1 MPa/s, and continues with this change until it is destroyed. Similarly, 7 (0.01 → 0.1), 7 (0.1 → 0.01), 8 (0.01 → 0.1), 8 (0.1 → 0.01) in Fig. 4 can deduce the rest from above examples, which are only the difference of the initial hydrostatic pressure.

Issue 3:
English should be checked again, there are some spelling mistakes in the paper, such as the semicolon in the abstract, the words after the comma should be lowercase, I suggest a native English speaker check it English before re-submission.

Discussion:
Thanks to the reviewer's suggestion, we sought the help of the translation company to polish the English, and the specific changes were marked in blue highlight.