Cyclic Loading and Unloading of Weakly Consolidated Sandstone with Various Water Contents
Round 1
Reviewer 1 Report
The current manuscript deals with understanding the strength aspects of weakly consolidated sandstone at different water contents subjected to cyclic loading/unloading relying on "Particle Flow Code Two Dimensional". The reviewer lauds the efforts of authors in trying to apply PFC2D (which is a numerical modeling software that simulates the behavior of granular materials, including sands and soils) to study the behavior. I have my serious queries which may require strong addressing from the authors while revising the manuscript by providing technically strong queries:
1. The entire abstract doesn’t capture the true essence of the work done. It seem tardy and misses out on quantitative and qualitative aspects of research findings like what is the threshold water content where the cyclic parameters are observed to be lowest? Without such observations reported in the abstract, it looks very redundant. The authors must comprehensively revise the entire abstract.
2. While PFC2D can be a powerful tool for studying the mechanical behavior of weakly consolidated sandstone under various loading conditions, it cannot address the following aspects very clearly. The authors must clearly understand the following queries and reply to the point with specific answers relying on the literature available in this aspect.
3. PFC2D models materials as discrete particles interacting through contact forces. While this approach is suitable for granular materials, it may not fully capture the complexities of weakly consolidated sandstone, which is a heterogeneous and porous material. Representing the material as a collection of discrete particles might not accurately reflect the actual behavior of the rock. How do the authors address this aspect for the current study? How can the results be applied to practical field conditions?
4. The accuracy of numerical simulations depends on the validity of the constitutive models used to describe the material behavior. PFC2D relies on specific constitutive models, and their applicability to weakly consolidated sandstone might be limited or not fully representative of the real material behavior. In such a scenario, how can the results provided be justified by authors?
5. PFC2D operates at a microscopic level, simulating interactions between individual particles. While it can provide insights into the microscale behavior of the material, it may not account for macroscopic phenomena that arise at larger scales, such as the effects of grain size distribution, sample size, and boundary conditions. In real field conditions, there will be high heterogeneity in soil particle sizes. What are the possible answers the authors can provide for each of these queries?
6. What is the rationale behind selecting mesoscopic parameters adopted in the study as reported in Table 1? Provide valid justification from published literature for each of these parameters.
7. What will be effect of fines on the behavior of weakly consolidated sandstones and how does it affect the mesoscopic parameters adopted in the study and how does it affect the fluid-particle interaction i.e., soil water characteristic features etc.? This aspect is very important. The authors are strongly encouraged to refer to the following articles while revising their paper and draw some critique to justify the claims made by them (https://doi.org/10.1007/s42107-023-00800-4; https://doi.org/10.1061/(ASCE)MT.1943-5533.0003114)
8. PFC2D's ability to simulate the influence of water content on weakly consolidated sandstone might be limited. The software typically does not fully consider the complex fluid-solid interactions that occur in porous media like sandstone, which can significantly affect the material's mechanical response. Did the authors check elsewhere in literature where such a study has been attempted for other soil types? The hysteresis associated with water content change cannot be predicted properly. The authors must address this aspect by referring to the articles which are suggested earlier for query No. 7 while revising this paper.
9. The complex boundary conditions and material properties which are chosen in the study might be specific to some episodic case and cannot be extended to other types of sandstones. This might limit the scale and scope of simulations that can be performed. How do the authors justify this aspect? The answer should be prompt and specific.
10. Properly calibrating the PFC2D model for weakly consolidated sandstone with various water contents can be challenging, and its accuracy may depend on the quality and availability of experimental data for comparison. What is the authenticity of the data used in the study? Provide valid justification.
11. Why didn’t the authors perform rapid dynamic loading scenarios, such as seismic events or impact loading using ‘PFC2D’ on the selected sandstone material? These aspects are quite relevant in some geological and engineering applications. Provide valid reasons for the same.
12. The entire conclusions section has to be redrafted by considering the above queries.
13. After the conclusions, provide takeaways from this work in the form of an end statement highlighting the practical importance of the study. This will appeal to the readership of Sustainability.
The authors must carefully address each of the queries raised by this reviewer while revising the manuscript. The final decision will be made based on the technically strong answers provided by the authors.
Author Response
Thanks for the valuable opinions of the experts, I have made changes to the article, please see the attachment.Author Response File: 
Author Response.pdf
Reviewer 2 Report
"Cyclic loading and unloading of weakly consolidated sand-stone with various water contents"
This manuscript presents the investigation results on the effects of loading and unloading on the mechanical properties of weakly cemented sandstone with various water contents. This manuscript is well organized and written. I think that it cen be accepted in this form.
"Cyclic loading and unloading of weakly consolidated sand-stone with various water contents"
This manuscript presents the investigation results on the effects of loading and unloading on the mechanical properties of weakly cemented sandstone with various water contents. This manuscript is well organized and written. I think that it cen be accepted in this form.
Author Response
Thanks to the valuable opinions of the experts, I revised the English of the article.Reviewer 3 Report
Comments on (Cyclic loading and unloading of weakly consolidated sandstone with various water)
Overall manuscript is very well written on an interesting topic. The main flaw is the methodology is not clearly mentioned in the manuscript. It is suggested to add the methodology as flow chart or in bullet steps. This makes easy for reader to understand the flow of research and can get more benefit from this research article.
The methodology must be added before section – 2.
The author must explain the experiments performed in laboratory and clearly distinguished between the simulated and experimental results, specifically in figures. While looking as figures (3, 4, 5 etc.) there is no mentioning that these are simulated results or laboratory results.
(Lines – 71 – 74): Kindly give a brief background for the “Particle Flow Code Two-Dimensional (PFC2D) program”.
For example, add: “PFC2D is based on the distinct element method (DEM), which is a numerical technique for simulating the interactions between discrete particles”. And so on.
(Line – 71) “…..dimensions of ф50 × 100 mm was ….” Is this dimension is correct. What will be the particle size (diameter of particles) in this model. This is confusing as ф is usually used for diameter, but in Figure – the model sample size is 50mmx100mm and in Table – 1, the particle size is mentioning as 0.35 mm. Please check it again and update/correct if required.
(Lines – 91 – 92) “…. and they are within an acceptable range for this study ….”. What is the acceptable range? Please elaborate it.
(Line – 136) “…exists as bound water, which causes erosion of the rock skeleton …” Here erosion is not the phenomena, kindly correct.
(Line – 150) “… which indicates that internal fracture compaction occurred…” In simulated samples, how the fractures have been induced. If these are actual sample then it can make a sense but for simulated samples, fractures must be induced and mention in the manuscript. Please explain. In case of unloading, due to relaxation of sample there are chances for induction of cracks/fractures.
Author Response
Thanks for the valuable opinions of the experts, I have made changes to the article, please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have addressed my comments raised during the first review. The reviewer is satisfied with their response and recommends acceptance of the revised version of the manuscript.
Author Response
感谢您的认可。
