Study on Damage Characteristics and Failure Patterns of Sandstone Under Temperature–Water Interactions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents the compressive strength of the sandstone at different temperatures (25℃, 55℃, 85℃, 95℃) and immersion duration (0.5h, 1h, 3h). The reader will find what the title describes. The manuscript is well organised. The references are properly chosen however, refer only to Chinese authors. The test results extend engineering knowledge. There is no new model. The methodology of the test was selected as the property. The results of the calculations support the conclusions.

The following shortcoming is:

1.      The introduction should be numbered as 1.

2.      The introduction. Is the compressive strength of the sandstone important only in tunnel construction in China?

3.      Line 131. The authors should explain the polyethene film and custom-made asbestone thermal covers in detail. In my opinion, it will influence the test results.

4.      Line 193. It is not ‘statistically calculated’. There is information about how many specimens were used for each test condition. From a statistical point of view, it should be presented as mean or mode, range (minimum and maximum), standard deviation etc.

5.      Chapter 3. Where are diagrams of strain-stress? There are only stress-time diagrams in Figure 3. How the reader will know when ended elastic part and starts plastic part of loading?

6.      Figure 7 (b). The legend of the abscess axis is not in English.

7.      Figure 8. It should be a scale the same for ordinate axes. It looks like the total energy is less than the dissipated energy.

8.      Equation (7). Why are there additional variables in the equation? Some comments should be given before the equation is written.

9.      Lines 326, 328, 329 and 333. What does rock the authors mean?

Author Response

1.Question: The introduction should be numbered as 1.

Response: Thank you very much for the comments from the reviewer. In accordance with your recommendations, we have revised the introduction number to 1 and renumbered the sections in the following text. Additionally, we have conducted a thorough review of the entire manuscript to ensure that similar issues do not recur. The modified parts are highlighted in red font, and the specific modifications are as follows:

Modification:

1. 1. Introduction
2. 2. Experimental methods

2.1. Sample preparation

2.2. Experimental plan

2.3. Experimental equipment and procedure

3. 3. Analysis of sandstone damage characteristics under different immersion times and temperatures
4. 4. Damage characterization of sandstone under different soaking times and temperatures

4.1. Energy evolution patterns of sandstones with different immersion times and temperatures

4.2. Sandstone damage characterization

5. 5. Analysis of sandstone failure characteristics under different soaking times and temperatures
6. 6. Discuss
7. 7. Conclusion

 

2.Question: The introduction. Is the compressive strength of the sandstone important only in tunnel construction in China?

Response: Thank you very much for the comments from the reviewer. In accordance with your recommendations, we have revised the introduction section and further expanded the engineering background related to the mechanical properties of rocks to better align with the engineering context of international tunnel construction. The specific modifications are detailed as follows:

Modification:

Modify “It is evident that many scholars have conducted research on the damage evolution, failure mechanisms, and theoretical analysis of rocks under the combined effects of temperature and water, and have achieved significant results.” to “It is evident that a wide range of scholars have conducted relevant research concerning the evolution of rock damage, destruction patterns, and theoretical analyses under the combined effects of temperature and water, achieving fruitful results. However, in current international and domestic transportation tunnel construction, the high ground temperatures encountered are generally below 100°C. The Seikan Tunnel, which crosses the seabed, faces a construction environment with high temperatures (up to 55°C), high pressure, and high water content. Similarly, the Gotthard Base Tunnel also encounters high temperatures (up to 46°C) and humid conditions during its construction. In the construction of the Sangzhuling Tunnel, temperatures can reach 89°C, while the temperatures in the tunnels of the Andes Mountains approach 100°C. However, there are few reports on the damage evolution and destruction patterns of sandstone with different water contents below 100°C. This study conducts uniaxial compression tests on sandstones with different soaking times (varying water contents) and temperatures (below 100°C) to investigate the alterations in sandstone mechanical properties influenced by temperature and water, analyze the damage and destruction characteristics of the sandstones, and establish a damage equation based on dissipated energy, thereby facilitating the examination of damage and destruction patterns of sandstone under the interactions of temperature and water.”

 

3.Question: Line 131. The authors should explain the polyethene film and custom-made asbestone thermal covers in detail. In my opinion, it will influence the test results.

Response: Thank you very much for the comments from the reviewer. The sample is insulated with polyethylene film and a homemade asbestos insulation shell. The asbestos insulation material is produced through a specific processing procedure, during which nano-sized silica aerogel particles are thoroughly integrated into ceramic glass fiber cotton. The polyethylene film is a standard market polyethylene film, and adhesive is employed to bond the custom aerogel mat to the polyethylene shell, forming the insulation device. During the loading process, it has minimal impact on the mechanical properties and deformation of the specimen ^[1-2].

Insulation device

[1]Zhang SJ, Li XB, Cheng JK, et al. Thermal-mechanical evolution characteristics of thermal insulation materials of rock true triaxial testing machines under complex working conditions[J].Gold Science and Technology, 2024, 32(04): 594-609. https://doi.org/10.11872/j. issn. 1005-2518.

[2]Xue SN, He ZQ, Li C,et al. Physical and mechanical properties of thermal insulation materials for in-situ temperature-preserved coring of deep rocks[J]. Coal Geology & Exploration, 2023,51(08):30-38.https://doi.org/10.11872/10.12363/issn.1001-1986.

 

4.Question: Line 193. It is not ‘statistically calculated’. There is information about how many specimens were used for each test condition. From a statistical point of view, it should be presented as mean or mode, range (minimum and maximum), standard deviation etc.

Response: Thank you very much for the comments from the reviewer. We have made modifications to the "statistical calculations" in the analysis of acoustic emission ringing, acoustic emission energy, and the cumulative ringing of acoustic emissions in the text. The specific modifications are detailed as follows:

Modification:

Modify “In order to more intuitively and clearly demonstrate the impact of different temperatures and soaking times on the acoustic emission damage characteristics of sandstone, the maximum acoustic emission ringing count, energy, and cumulative acoustic emission ringing count for sandstone under different temperatures and soaking times were statistically calculated, as illustrated in Figure 4.” to “In order to more intuitive and precise representation of the impact of varying temperatures and soaking durations on the acoustic emission damage characteristics of sandstone, we undertook a comprehensive quantitative analysis of the maximum acoustic emission ring count, energy, and cumulative ring count of sandstone subjected to different thermal conditions and soaking times. The findings are illustrated in Figure 5.”

 

5.Question: Chapter 3. Where are diagrams of strain-stress? There are only stress-time diagrams in Figure 3. How the reader will know when ended elastic part and starts plastic part of loading?

Response: Thank you very much for the comments from the reviewer. The energy-strain curves and stress-strain curves in Section 3 are presented in Figures 5, 6, and 7. Figure 3 shows the stress-time curve and the acoustic emission-time curve, which aims to better analyze the variation of stress and acoustic emission parameters over time during the failure process of red sandstone under uniaxial compression. In the analysis of Section 4.2, the stress-strain curve is divided into the compaction stage, elastic stage, plastic stage, and post-peak stage, where the elastic stage is represented by the linear segment of the stress-strain curve, and the boundary point of the elastoplastic stage is where the slope of the line changes. The division in Section 5 follows a similar structure.

 

6.Question: Figure 7 (b). The legend of the abscess axis is not in English.

Response: Thank you very much for the comments from the reviewer. During the writing process of the article, there was an error in the horizontal coordinates of the elastic modulus of sandstone soaked for 3 hours at different temperatures. The relevant content has been revised, and the specific modifications are as follows:

Modification:

 

Figure 8（b）U^e

 

7.Question: Figure 8. It should be a scale the same for ordinate axes. It looks like the total energy is less than the dissipated energy.

Response: Thank you very much for the comments from the reviewer. We have modified Figure 8 to Figure 9 (a) by employing a consistent coordinate scale for total energy, potential energy, and dissipated energy. Additionally, we have provided a local magnification of the dissipated energy curve. These modifications are intended to facilitate a more comprehensive analysis of the variation patterns of the different energy curves. The specific modifications are as follows:

Modification:

 

Figure 9（a） Plot of energy changes in sandstone at different temperatures and immersion times

 

8.Question: Equation (7). Why are there additional variables in the equation? Some comments should be given before the equation is written.

Response: Thank you very much for the comments from the reviewer. We have added comments before writing the equations and cited relevant references. The specific modifications are as follows:

Modification:

However, the sandstone retains its load-bearing capacity in the post-peak stage. To reflect the existence of the rock's residual strength, a correction factor is introduced. By modifying the relationship between dissipated energy and the damage variable, the damage variable D does not completely reach 1 in the post-peak stage, thereby more precise representation of the damage evolution characteristics of sandstone. Consequently, modifications are made to equation (6) ^[26-27].

[26] Dang YQ, Wu YM, Wang TJ, et al. Energy and Damage Evolution Characteristics ofRock Materialsunder Different Water Contents[J]. Chinese Journal of High Pressure Physics, 2023, 37(03): 62-71. https://doi.org/10.11858/gyw1zb.20220699.

[27] Liu DQ, Guo XP, et al. experimental study on damage and failure energy evolution of brittle rocks under uniaxial compression[J]. Journal of Engineering Geology, 2023, 31(3): 843-853. https://doi.org/10.13544/j.cnki.jeg.2022-0799

 

9.Question: Lines 326, 328, 329 and 333. What does rock the authors mean?

Response: Thank you very much for the comments from the reviewer. We have added comments before writing the equations and cited relevant references. The specific modifications are as follows:

Modification:

From Figure 9, it is evident that the damage variable accurately represents the stress-strain behavior of the sandstone. During the compaction stage, under external force, the initial cracks inside the sandstone close, and the dissipated energy shows little change, with the damage variable remains nearly almost constant. In the elastic stage, a significant portion of the energy input into the sandstone is stored as elastic energy, while a small fraction allocated for crack development. During this stage, the damage variable increases slightly, but the increase is minimal. In the plastic stage, the sandstone begins to undergo plastic deformation, and the initiation and development of new cracks require significant energy, leading to a gradual increase in the damage variable with fluctuating changes, which indicates that the damage to the sandstone is intensifying. In the post-peak stage, when the stress exceeds the peak strength of the sandstone, the internal cracks continue to develop, resulting in macroscopic damage, with through cracks forming, a large release of elastic energy, and a sharp increase in dissipated energy. The damage variable shows a sudden increase but does not reach 1, indicating that the sandstone has not been completely destroyed after the peak and still retains some bearing capacity.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Manuscript number: applsci-3320056.

Paper Topic: Study on Damage Characteristics and Failure Patterns of Sandstone under Temperature-Water Interactions.

The manuscript investigates the characterization of damage using uniaxial compression tests on sandstone, a potential host rock for a high-temperature, water-rich tunnel in southern Tibet. Authors have used mild temperature ranges (25℃, 55℃, 85℃, 95℃) and immersion durations (0.5h, 1h, 3h) under the heating and cooling method. The authors also measured the acoustic emission (AE) during uniaxial compression. The complex temperature variations designed in the tests are unlikely to correspond to an actual in-situ background. The lack of innovation—please note the different cooling treatment after mild temperature treatment—is not an innovative point; a reasonable thermal and cooling path matters more than a complex heating and cooling path without any in-situ sense. The author could improve the paper's writing by making certain parts more readable and potentially shortening the document. Some relevant references, especially those published in the heating-cooling treatment, are missing. Otherwise, this paper is unlikely to address the research gap. However, the manuscript requires a major revision before publication, as outlined below.

1. The author should reorganize the introduction section by reducing the background part and reviewing more relevant literature, which helps identify the research gap. We recommend reviewing studies on the effects of heating-cooling rates and grain size on the thermo-physical properties of sandstone. Probably underground high geothermal temperature, groundwater, and high ground stress-based are to correlate your result to thermal cracks due to grain expansion during heating treatment and grain contraction during cooling.
2. The method should be described more clearly, especially the following points.
3. Please explain the experimental procedure in the text, describe the experimental setup and technical details of the acoustic emission nano 30 sensor, and include the experimental plan in a graph. How have the authors calibrated the experimental device? What is the precision and calibration of the measurements, including the error calculation?
4. The method the authors have adopted for heating the samples is questionable. What is the appropriate heating and cooling rate for the specimen in this paper, and how long should we hold the sandstone at the target temperature? The specimen may not have an evenly distributed temperature. To ensure that the entire sample reaches the target temperature, one could install a thermocouple touching it.
5. Explain why different thermal treatments (25℃, 55℃, 85℃, 95℃) and immersion durations (0.5h, 1h, 3h) under the heating and cooling method are chosen for the experiments and what the expected outcome in a real-time scenario is. Provide a thorough explanation, free from any assumptions, about the possibility of thermal cracking resulting from grain contraction under varying cooling conditions.
6. Briefly explain and rewrite the experimental procedure in the text and include the experimental plan in a graph. I believe it would be beneficial for the authors to provide a detailed explanation of how the results vary with temperature. It should be clear that the authors have tested sandstone specimens that include either borehole samples or surface outcrop samples.

1. Line 306, "cumulative accumulated dissipated energy," lacks clarity.
2. You may need to clearly explain or discuss the following two questions from your data set after the heating and cooling treatment.

1. What caused variation of physical/mechanical properties between sandstone samples?
2. What causes the dependence of heating and cooling treatments on thermal and physical properties?

• Researchers have thoroughly investigated the effects of grain expansion during the heating process on the thermo-physical properties of sandstone. What are the effects of grain contraction during the cooling process?

11. Provide the mineralogical composition of the sandstone samples (after heating and cooling treatment). This would serve as solid evidence for the discussion section.

1. The authors must elucidate how these findings integrate into the overarching framework of damage theory in rocks and the practical implications of their insights, particularly in geothermal applications. In what ways does this work enhance current hypotheses on rock damage due to thermal stress, and what are the ramifications for geological applications?

13. The results are mixed with discussion. The results section presents the descriptions of the data. The discussion section provides explanations, comparisons, implications, and/or limitations based on the results.
14. The conclusion and abstract should undergo a revision. Write the content and the numerical values; improve the conclusion and abstract section by incorporating the significant thermal-physical changes at different temperatures due to associated thermal cracking (discussed in the discussion section).

    Following references is very helpful how to estimate thermal property from mineral composition

    1.       Gautam, P. K., Singh, S. P., Agarwal, A., & Singh, T. N. (2022). Thermomechanical characterization of two Jalore granites with different grain sizes for India’s HLW disposal. Bulletin of Engineering Geology and the Environment, 81(11), 1-26.

    2.       Sirdesai, N. N., Gupta, T., Singh, T. N., & Ranjith, P. G. (2018). Studying the acoustic emission response of an Indian monumental sandstone under varying temperatures and strains. Construction and Building Materials, 168, 346-361.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

NA

Author Response

1.Question: The author should reorganize the introduction section by reducing the background part and reviewing more relevant literature, which helps identify the research gap. We recommend reviewing studies on the effects of heating-cooling rates and grain size on the thermo-physical properties of sandstone. Probably underground high geothermal temperature, groundwater, and high ground stress-based are to correlate your result to thermal cracks due to grain expansion during heating treatment and grain contraction during cooling.

Response: Thank you for your valuable comments. We reduced the length of the background content in the introduction section, added studies on the effects of heating-cooling rates and grain size on the thermal physical properties of sandstone, and also increased the effects of high underground temperature, water, and high in-situ stress on rocks. The modified parts in the text are marked in red, and the specific modifications are as follows:

Modification:

1. Introduction

Modify“With the rapid development of the transportation industry in China, the number and scale of traffic tunnels have been increasing. In tunnel construction in Western China, the surrounding rock is often subjected to a complex geological environment, frequently influenced by high geothermal temperatures, groundwater, and high ground stress.”to“With the rapid development of global transportation, the geological challenges faced in tunnel construction are becoming increasingly severe. In high geothermal and water-rich environments, the surrounding rock of tunnels is frequently exposed to the combined effects of high temperature and water, resulting in significant rock corrosion and fatigue deterioration. This results in deformation, instability, and potential collapse, causing engineering disasters. Consequently, It is essential to investigate the damage evolution and failure mechanisms of rock under the combined effects of high temperature and water is particularly important for the safety and stability of tunnel construction.

Currently, numerous scholars have conducted extensive research on the damage mechanisms and failure characteristics of rocks under the effects of temperature, water, or their combined effect. Sirdesai et al. [1] conducted uniaxial compression tests on sandstone at temperatures ranging from 200°C to 1000°C and found that the expansion of mineral grains and anisotropy lead to changes in the physical and mechanical properties of the sandstone. Pradeep et al. [2] studied the mechanical and mineralogical changes in granite with different grain sizes under the effect of temperature, revealing that grain expansion was the cause of the mechanical property changes, with coarse-grained granite being more significantly affected. Pan et al. [3] examined the effects of different cooling media on the mechanical properties of granite and limestone at temperatures ranging from 25°C to 800°C, discovering that air cooling had a minimal impact on the mechanical properties, while all cooling media caused a degradation in the compressive strength of the rocks. Cai et al. [4] performed Brazilian splitting tests on high-temperature granite (150°C-600°C) under two cooling methods, natural cooling and liquid nitrogen cooling, and found that liquid nitrogen cooling effectively promoted the development of internal cracks in high-temperature granite and reduced its mechanical properties. Cui et al. [5] analyzed the damage evolution of granite under thermal cycling at 400°C, observing that as the number of heating-cooling cycles increased, the weight loss rate and volume expansion rate of the granite increased exponentially, while the evolution of internal micro-cracks was described using acoustic emission parameters. These studies show that various high-temperature conditions and cooling methods significantly influence the mechanical properties of rocks, leading to a reduction in strength, crack propagation, and degradation of internal structures. In studies on the effects of water on rocks, HU et al. [6] investigated the impact of different water contents on the damage characteristics of red sandstone, finding that higher water content led to greater damage, and derived a damage constitutive model for sandstone at different water contents using Lemaitre’s model. Azhar et al. [7], using sandstone from the Lanzhou water supply project crossing highly clayey sandstone, conducted uniaxial compression tests under different soaking times and combined XRD and SEM techniques, concluding that water absorption and softening were the reasons for the reduced durability of the sandstone. Wasantha et al. [8] used ARAMIS to study the damage evolution of sandstone under dry and saturated conditions, discovering that the quartz content significantly influenced the water-weakening effect, and higher clay content resulted in more significant damage. Alomari et al. [9] conducted uniaxial and triaxial compression tests on sandstone from Wyoming, USA, and developed a predictive model for compressive strength based on water content and grain size, finding that as water content and grain size increased, the compressive strength of the sandstone decreased. Zhao et al. [10] studied the post-peak mechanical behavior of sandstone under water-pressure coupling, observing that peak strength and residual strength decreased as water pressure increased, and established a predictive model for the post-peak strength of sandstone under different water pressures. Roy et al. [11] investigated the effects of water content on the mechanical properties and fracture behavior of three different types of shale, finding that higher water content led to lower strength and greater susceptibility to fracture. These studies demonstrate that higher water content and larger grain sizes both contribute to a reduction in rock strength and an exacerbation of its damage, while an increase in water pressure further decreases both peak strength and residual strength. Regarding the combined effects of temperature and water on rocks, Ping Qi et al. [12] conducted temperature-water coupling experiments on sandstone with varying internal ring diameters, discussing the influence of temperature and water on sandstone damage and degradation. However, they did not consider the effects of different temperatures, and the experimental conditions differed from real construction environments. Yan Minghui et al. [13] subjected granite to thermal-liquid coupling treatments and used uniaxial compression tests to examine the physical and mechanical damage caused by thermal-liquid-mechanical coupling. Yang et al. [14] conducted water-rock interaction tests on heat-treated granite under high temperatures and pressures, observing that thermal expansion initially increased permeability, which later decreased. Wang Chun et al. [15], focusing on deep geothermal energy exploitation, used Hopkinson bar tests to conduct dynamic tests under thermal-water-mechanical conditions, establishing a damage model based on deformation characteristics and revealing the dynamic damage failure patterns of rocks. Zheng et al. [16] analyzed the effects of temperature-water coupling on coal samples, finding that as the temperature increased, the coal’s energy storage capacity initially decreased and then increased. These studies demonstrate that the combined effect of temperature and water intensifies rock damage, affects its energy storage capacity, and causes changes in permeability due to thermal expansion.

It is evident that a wide range of scholars have conducted relevant research concerning the evolution of rock damage, destruction patterns, and theoretical analyses under the combined effects of temperature and water, achieving fruitful results. However, in current international and domestic transportation tunnel construction, the high ground temperatures encountered are generally below 100°C. The Seikan Tunnel, which crosses the seabed, faces a construction environment with high temperatures (up to 55°C), high pressure, and high water content. Similarly, the Gotthard Base Tunnel also encounters high temperatures (up to 46°C) and humid conditions during its construction. In the construction of the Sangzhuling Tunnel, temperatures can reach 89°C, while the temperatures in the tunnels of the Andes Mountains approach 100°C. However, there are few reports on the damage evolution and destruction patterns of sandstone with different water contents below 100°C. This study conducts uniaxial compression tests on sandstones with different soaking times (varying water contents) and temperatures (below 100°C) to investigate the alterations in sandstone mechanical properties influenced by temperature and water, analyze the damage and destruction characteristics of the sandstones, and establish a damage equation based on dissipated energy, thereby facilitating the examination of damage and destruction patterns of sandstone under the interactions of temperature and water.

 

2.Question: The method should be described more clearly, especially the following points.

Response: Thank you for your valuable comments. We have provided a more comprehensive introduction to the areas of concern in accordance with your request.

 

3.Question: Please explain the experimental procedure in the text, describe the experimental setup and technical details of the acoustic emission nano 30 sensor, and include the experimental plan in a graph. How have the authors calibrated the experimental device? What is the precision and calibration of the measurements, including the error calculation?

Response: Thank you for your valuable comments. We have provided a detailed description of the experimental process in the text. A total of six Nano 30 acoustic emission sensors were arranged in the experiment, divided into two layers, with three Nano 30 sensors evenly distributed on each layer. The upper and lower layers were arranged with a 90° staggered distribution, and the Nano 30 sensors were placed 20 mm away from the upper and lower end faces. The specific positions are shown in Flowchart 3. The acoustic emission bandwidth ranged from 125 kHz to 750 kHz, and the preamplifier model was 2/4/6 with amplification factors of 20, 40, and 60. For this experiment, the setting was 40 to ensure measurement accuracy. Calibration was performed before the experiment using pencil lead break testing, with the standard being stable, clear, and noise-free collected signals. The modified parts in the text are marked in red, and the specific modifications are as follows:

Modification:

2.3 Experimental equipment and procedure

Modify“The uniaxial compression tests on sandstone were conducted using a WAW-1000B electro-hydraulic servo universal testing machine with a loading rate of 0.2 mm/min. Strain data were collected using a DH3820 strain acquisition system, while acoustic emission (AE) data were recorded using the AE win Express8 acoustic emission acquisition system.”to“The experimental process is divided into three stages: the preparation stage, the sandstone soaking stage, and the uniaxial loading stage. (1) Preparation stage: The sandstone is processed into cylindrical specimens with dimensions of ø50mm × 100mm, as shown in Figure 3(a). After processing, the red sandstone is placed into a drying oven, heated at a rate of 4°C/min to 105°C, and dried for 24 hours, as shown in Figure 3(b). Then, the specimens are cooled to room temperature at a rate of 0.5°C/min. (2) Sandstone soaking stage: The mass of the red sandstone after drying, denoted as m0, is measured. The specimens are then placed into a constant temperature water tank set to the target temperatures (25°C, 55°C, 85°C, and 95°C). At each target temperature, the sandstone specimens are soaked for 0.5h, 2h, and 3h, as shown in Figure 3(c), and the mass of the red sandstone after soaking, denoted as m1, is measured. (3) Uniaxial loading stage: The sandstone specimens, after soaking, are immediately placed into a homemade insulation device, as shown in Figure 3(i). Uniaxial compression is performed using the WAW-1000B electro-hydraulic servo universal testing machine, as shown in Figure 3(e), with a loading rate of 0.2mm/min. Real-time monitoring is conducted using the AEwin Express8 acoustic emission system, as shown in Figure 3(f), and strain data is collected using the DH3820 strain acquisition system, as shown in Figure 3(g). The Nano 30 sensors, shown in Figure 3(d), are arranged in two layers, with three sensors in each layer, positioned in a 90° staggered pattern. The distance between the probes and the top and bottom faces is 20mm. The acoustic emission bandwidth ranges from 125kHz to 750kHz, and the preamplifier models are 2/4/6, with amplification factors of 20, 40, and 60, respectively, with the test set to 40 to ensure measurement accuracy. Calibration is performed before the experiment by using the lead-breaking operation to ensure that the collected signals are stable, clear, and free from noise. The specific experimental procedure is shown in Figure 3.”

Figure 3 Test process and operation steps

(a) Sandstone specimen (b) Electric heating constant temperature drying oven (c) Warm water tank (d) Nano 30 sensor arrangement (e) WAW-1000B electro-hydraulic servo universal testing machine (f) AEwin Express8 acoustic emission system (g) Donghua DH3820 stress-strain acquisition system (h) Nano sensor (i) Insulation device (j) Radial stress sensor (k) Strain gauge (l) Sandstone in the experiment

 

4.Question: Please explain the experimental procedure in the text, describe the experimental setup and technical details of the acoustic emission nano 30 sensor, and include the 们的experimental plan in a graph. How have the authors calibrated the experimental device? What is the precision and calibration of the measurements, including the error calculation?

Response: Thank you for your valuable comments. Different heating and cooling rates and holding times do indeed significantly affect the experimental results. In this experiment, the heating rate of the electric thermostatic oven was set to 4℃/min to ensure uniform heating of the sample. Water immersion leads to an uneven temperature distribution inside the sandstone. Our primary focus was on the combined effects of different temperatures and immersion durations on the damage and failure characteristics of sandstone. The water bath heating method is more effective in achieving the temperature-water interaction. Therefore, the temperatures and immersion durations determined in this study were 25℃, 55℃, 85℃, 95℃ and 0.5 h, 1 h, 3 h, respectively.

To minimize the influence of the initial moisture content of the sandstone specimens on the experimental results, the selected sandstone was subjected to drying treatment. After drying, the specimens were cooled at a rate of 0.5℃/min, ensuring that the cooling rate did not impact the experiment. The water bath heating method was subsequently employed to investigate the combined effects of temperature and immersion duration. The sandstone was immersed at 25℃, 55℃, 85℃, and 95℃ for 0.5 h, 1 h, and 3 h, respectively. Finally, a thermal insulation device was used to reduce heat loss, and uniaxial compression tests were conducted.

 

5.Question: Explain why different thermal treatments (25℃, 55℃, 85℃, 95℃) and immersion durations (0.5h, 1h, 3h) under the heating and cooling method are chosen for the experiments and what the expected outcome in a real-time scenario is. Provide a thorough explanation, free from any assumptions, about the possibility of thermal cracking resulting from grain contraction under varying cooling conditions.

Response: Thank you for your valuable comments. In current international and domestic transportation tunnel construction, the high ground temperatures encountered are generally below 100℃. For example, the Seikan Tunnel faced high temperature (up to 55℃), high pressure, and high-water-content conditions during its construction under the seabed. Similarly, the Gotthard Base Tunnel encountered high temperatures (up to 46℃) and humid conditions during its construction. The temperature in the Sang Zhuling Tunnel reached 89℃, while the Andes Tunnel approached 100℃. According to the Chinese Technical Specifications for Highway Tunnel Construction (JTG 3370.1-2018), tunnels with temperatures exceeding 28℃ are defined as high-temperature tunnels. To compare with normal temperatures (25℃), this study set four temperature levels: 25℃, 55℃, 85℃, and 95℃. As temperature increases, the interaction between water and the mineral structure is enhanced, which increases the water absorption effect of the rock. According to references [17-20], sandstone becomes saturated after 3 hours of water immersion. Therefore, three immersion durations were set: unsaturated (0.5 h, 1 h) and saturated (3 h). This study aims to conduct uniaxial compression tests on sandstone under different immersion durations (with varying water content) and different temperatures (below 100℃) to explore the mechanical property changes of rocks under the combined effects of temperature and water. It also seeks to analyze the damage and failure characteristics of rocks and establish a damage equation based on dissipated energy. The goal is to analyze the mechanical behavior, damage characteristics, and failure patterns of sandstone under the combined effects of temperature and water in complex environments (high geothermal and high-water-content conditions).

The modified parts in the text are marked in red, and the specific modifications are as follows:）

Modification:

2.2. Experimental plan

Modify“The samples were then placed in a water bath for immersion at different temperatures and durations. According to the literature [13-14], the water content of sandstone reaches near saturation after 3 hours of immersion. Therefore, this experiment was designed with three soaking durations (0.5h, 1h, and 3h), and four temperatures (25°C, 55°C, 85°C, and 95°C) for each soaking duration.” to“The "Technical Specification for Highway Tunnel Construction" (JTG 3370.1-2018) in China defines tunnels with temperatures exceeding 28°C as high-temperature tunnels. In this study, four temperatures—25°C, 55°C, 85°C, and 95°C—were established for comparison against the standard temperature of 25°C. According to references [17-20], sandstone reaches saturation after 3 hours of soaking, and temperature increase enhances the interaction between water and the mineral structure, strengthening the water absorption effect of the rock. Therefore, three soaking durations were set: unsaturated (0.5h, 1h) and saturated (3h). Initially, an electric constant temperature box was employed to heat the sandstone at a rate of 4°C/min to 105°C, where it was held for 24 hours to remove the original moisture within the specimens. Subsequently, the temperature was decreased at a rate of 0.5°C/min to reduce thermal shock and ensure that only the thermal gradient influenced thermal cracking. Following this, the sandstone was subjected to a water bath at varying temperatures and times using a warm water tank. After heating the sandstone specimens to the target temperature and time, the specimens were removed and immediately insulated using polyethylene film and a homemade asbestos insulation shell. (The polyethylene film used is a common commercial polyethylene film. The asbestos insulation shell is made through a specific processing procedure, where nano-sized silica aerogel particles are fully integrated into ceramic fiberglass cotton. The customized aerogel felt is bonded to the polyethylene shell using adhesive.) Finally, the combined effects of temperature, water, and time on the damage and failure of sandstone were investigated using uniaxial compression and acoustic emission systems. The specific experimental scheme is shown in Table 1. For example, H-25-0.5 represents a sandstone specimen at 25°C with a soaking time of 0.5 hours.”

 [17] Fang J, Yao QL, Wang WN, et al. Experimental study on damage characteristics of siltstone under water action[J]. Journal of China Coal Society, 2018, 43(S2): 412-419. http://doi.org/10.13225/j.cnki.jccs.2018.0629.

[18] Yu C, Tang S, Duan D, et al. The effect of water on the creep behavior of red sandstone[J]. Engineering Geology, 2019, 253: 64-74. http://doi.org/10.1016/j.enggeo.2019.03.016.

[19] Xu Y, Li X, et al. Experimental study on the permeability evolution of argillaceous sandstone under elevated temperatures[J]. Engineering Geology, 2023, 313: 106974. http://doi.org/10.1016/j.enggeo.2022.106974.

[20] Wang Fei,Cao Ping,Cao Ri-hong,et al. The influence of temperature and time on water-rock interactions based on the morphology of rock joint surfaces[J]. Bulletin of Engineering Geology and The Environment,2019,78(5):3385-3394. http://doi.org/10.1007/s10064-018-1315-5

 

6.Question: Briefly explain and rewrite the experimental procedure in the text and include the experimental plan in a graph. I believe it would be beneficial for the authors to provide a detailed explanation of how the results vary with temperature. It should be clear that the authors have tested sandstone specimens that include either borehole samples or surface outcrop samples.

Response: Thank you for your valuable comments. We have revised the experimental procedures and schemes in the text and reanalyzed the variation patterns of the experimental results with temperature in Sections 3 and 6. The sandstone used in the experiments was sampled from a high geothermal and water-rich tunnel in southern Tibet, not from surface outcrop samples, which has been corrected in the text.

The modified parts in the text are marked in red, and the specific modifications are as follows:

Modification:

2.3 Experimental equipment and procedure

Modify“The uniaxial compression tests on sandstone were conducted using a WAW-1000B electro-hydraulic servo universal testing machine with a loading rate of 0.2 mm/min. Strain data were collected using a DH3820 strain acquisition system, while acoustic emission (AE) data were recorded using the AE win Express8 acoustic emission acquisition system.”to

2.2. Experimental plan

The "Technical Specification for Highway Tunnel Construction" (JTG 3370.1-2018) in China defines tunnels with temperatures exceeding 28°C as high-temperature tunnels. In this study, four temperatures—25°C, 55°C, 85°C, and 95°C—were established for comparison against the standard temperature of 25°C. According to references [17-20], sandstone reaches saturation after 3 hours of soaking, and temperature increase enhances the interaction between water and the mineral structure, strengthening the water absorption effect of the rock. Therefore, three soaking durations were set: unsaturated (0.5h, 1h) and saturated (3h). Initially, an electric constant temperature box was employed to heat the sandstone at a rate of 4°C/min to 105°C, where it was held for 24 hours to remove the original moisture within the specimens. Subsequently, the temperature was decreased at a rate of 0.5°C/min to reduce thermal shock and ensure that only the thermal gradient influenced thermal cracking. Following this, the sandstone was subjected to a water bath at varying temperatures and times using a warm water tank. After heating the sandstone specimens to the target temperature and time, the specimens were removed and immediately insulated using polyethylene film and a homemade asbestos insulation shell. (The polyethylene film used is a common commercial polyethylene film. The asbestos insulation shell is made through a specific processing procedure, where nano-sized silica aerogel particles are fully integrated into ceramic fiberglass cotton. The customized aerogel felt is bonded to the polyethylene shell using adhesive.) Finally, the combined effects of temperature, water, and time on the damage and failure of sandstone were investigated using uniaxial compression and acoustic emission systems. The specific experimental scheme is shown in Table 1. For example, H-25-0.5 represents a sandstone specimen at 25°C with a soaking time of 0.5 hours. The calculation formula for the water content of the sandstone specimen is:

                                                                                                （1）

Where: is the water content,  is the mass of the sandstone after soaking,  is the mass of the sandstone before soaking, with the unit in grams (g).

 

Table 1: Experimental Plan and Moisture Content of Sandstone at Different Immersion Times and Temperatures

Numbering	Temperature /°C	Soaking time /h	Water content	Numbering	Temperature /°C	Soaking time /h	Water content
H-25-0.5	25	0.5	1.04	H-85-0.5	85	0.5	1.02
H-25-1	25	1	1.62	H-85-1	85	1	1.56
H-25-3	25	3	2.02	H-85-3	85	3	2.91
H-55-0.5	55	0.5	1.37	H-95-0.5	95	0.5	1.21
H-55-1	55	1	1.71	H-95-1	95	1	1.43
H-55-3	55	3	3.01	H-95-3	95	3	2.68

 

The experimental process is divided into three stages: the preparation stage, the sandstone soaking stage, and the uniaxial loading stage. (1) Preparation stage: The sandstone is processed into cylindrical specimens with dimensions of ø50mm × 100mm, as shown in Figure 3(a). After processing, the red sandstone is placed into a drying oven, heated at a rate of 4°C/min to 105°C, and dried for 24 hours, as shown in Figure 3(b). Then, the specimens are cooled to room temperature at a rate of 0.5°C/min. (2) Sandstone soaking stage: The mass of the red sandstone after drying, denoted as m0, is measured. The specimens are then placed into a constant temperature water tank set to the target temperatures (25°C, 55°C, 85°C, and 95°C). At each target temperature, the sandstone specimens are soaked for 0.5h, 2h, and 3h, as shown in Figure 3(c), and the mass of the red sandstone after soaking, denoted as m1, is measured. (3) Uniaxial loading stage: The sandstone specimens, after soaking, are immediately placed into a homemade insulation device, as shown in Figure 3(i). Uniaxial compression is performed using the WAW-1000B electro-hydraulic servo universal testing machine, as shown in Figure 3(e), with a loading rate of 0.2mm/min. Real-time monitoring is conducted using the AEwin Express8 acoustic emission system, as shown in Figure 3(f), and strain data is collected using the DH3820 strain acquisition system, as shown in Figure 3(g). The Nano 30 sensors, shown in Figure 3(d), are arranged in two layers, with three sensors in each layer, positioned in a 90° staggered pattern. The distance between the probes and the top and bottom faces is 20mm. The acoustic emission bandwidth ranges from 125kHz to 750kHz, and the preamplifier models are 2/4/6, with amplification factors of 20, 40, and 60, respectively, with the test set to 40 to ensure measurement accuracy. Calibration is performed before the experiment by using the lead-breaking operation to ensure that the collected signals are stable, clear, and free from noise. The specific experimental procedure is shown in Figure 3.

Figure 3 Test process and operation steps

(a) Sandstone specimen (b) Electric heating constant temperature drying oven (c) Warm water tank (d) Nano 30 sensor arrangement (e) WAW-1000B electro-hydraulic servo universal testing machine (f) AEwin Express8 acoustic emission system (g) Donghua DH3820 stress-strain acquisition system (h) Nano sensor (i) Insulation device (j) Radial stress sensor (k) Strain gauge (l) Sandstone in the experiment

 

3.Analysis of sandstone damage characteristics under different immersion times and temperatures

As shown in Figure 5, at the same temperature, as the soaking time increases, the maximum AE ring count, maximum AE energy, and cumulative AE ring count of sandstone gradually decrease. When soaked for 3 hours, the acoustic emission signals (ring count, energy) and cumulative ring count of sandstone at all temperature conditions reach their minimum values. At the same soaking time, as the temperature rises, for soaking durations of 0.5 hours and 1 hour, the maximum AE ring count and maximum AE energy of sandstone exhibit a pattern characterized by an initial increase, followed by a decrease, and subsequently a further increase. In contrast, the cumulative AE ring count exhibits a gradual upward trend. For soaking durations of 3 hours at different temperatures, the maximum AE ring count, maximum energy, and cumulative AE ring count of sandstone all gradually increase with rising temperature.

With the increase in soaking time, the water content of sandstone gradually rises. High water content enhances the plastic deformation capacity of sandstone and reduces its brittleness failure degree, leading to a significant decrease in the acoustic emission signal values. This is the reason why the maximum AE ring count, maximum AE energy, and cumulative AE ring count of sandstone are all at their minimum after soaking for 3 hours. At the same soaking time but different temperatures, the water content of sandstone is highest at 55°C, resulting in weakened brittleness and enhanced plasticity of the sandstone, the sandstone exhibits a greater accumulation of energy prior to reaching the peak stress. Consequently, when failure occurs in the sandstone near the peak stress, it generates more pronounced acoustic emission signals. When the temperature further increases (above 55°C), on the one hand, the thermal expansion effect of the rock begins to appear, and on the other hand, the temperature continues to promote an increase in the water content of sandstone. The water content of the rock initially decreases and subsequently increases, resulting in a corresponding trend in the maximum ring count and maximum energy, which also exhibit a trend of first decreasing and then increasing. After soaking for 3 hours, high temperatures promote the further development of the thermal expansion effect in sandstone, causing more original microcracks to close, thereby significantly increasing the ring count and energy of the acoustic emission signals [23].

 

6.Discuss

This study employs the WAW-1000B electro-hydraulic servo universal testing machine loading system to carry out uniaxial compression tests on sandstone samples subjected to different temperatures (25°C, 55°C, 85°C, 95°C) and soaking durations (0.5 hours, 1 hour, 3 hours). Additionally, an acoustic emission system is used to study the damage and failure characteristics of sandstone under the combined influence of temperature and water. The findings indicate that at 85°C and 95°C, the thermal expansion effect of sandstone is more evident, leading to a decrease in the rock's permeability and water absorption capacity. In contrast, at 25°C and 55°C, the thermal expansion effect of sandstone is relatively less pronounced, which promotes water infiltration and results in a higher moisture content [29-33]. High moisture content exacerbates the dissolution [34-35], softening [36-38], and stress corrosion effects [39-40] of sandstone mineral particles, causing a decline in their mechanical properties. As the soaking duration increases, sandstone samples soaked for 3 hours exhibit the highest moisture content, which intensifies their softening and damage. This results in maximum damage to the sandstone, making the mineral particles within the rock more susceptible to external forces and facilitating the initiation and propagation of cracks.）

The research results indicate that the damage to rocks in high-temperature and water-saturated environments is not solely the result of increased temperature or prolonged immersion time, but rather the result of the interaction between the two factors. This finding further reveals the damage and failure mechanisms of sandstone under the combined effects of high temperature and water, particularly the comprehensive impact of different temperatures on the thermal expansion and moisture migration of sandstone. The experiments found that 55°C is the threshold for sandstone damage, indicating that there is a turning point in the thermal expansion effect of sandstone across different temperature ranges. This means that an increase in temperature does not always uniformly affect moisture migration; instead, there are both enhancing and inhibiting effects. This finding provides a new perspective for studying the damage mechanisms of rocks in high-temperature environments and offers theoretical support for establishing more accurate rock damage models. From an engineering perspective, the research results are significant for tunnel construction in high-temperature, water-rich environments. In practical construction, special attention should be paid to the stability of surrounding rock in such temperature ranges. Measures such as optimizing drainage systems, enhancing the impermeability of surrounding rock, and implementing effective reinforcement measures can be employed to mitigate the damage to sandstone caused by high moisture content, thereby reducing the likelihood of accidents.

[17] Fang J, Yao QL, Wang WN, et al. Experimental study on damage characteristics of siltstone under water action[J]. Journal of China Coal Society, 2018, 43(S2): 412-419. http://doi.org/10.13225/j.cnki.jccs.2018.0629.

[18] Yu C, Tang S, Duan D, et al. The effect of water on the creep behavior of red sandstone[J]. Engineering Geology, 2019, 253: 64-74. http://doi.org/10.1016/j.enggeo.2019.03.016.

[19] Xu Y, Li X, et al. Experimental study on the permeability evolution of argillaceous sandstone under elevated temperatures[J]. Engineering Geology, 2023, 313: 106974. http://doi.org/10.1016/j.enggeo.2022.106974.

[20] Wang Fei,Cao Ping,Cao Ri-hong,et al. The influence of temperature and time on water-rock interactions based on the morphology of rock joint surfaces[J]. Bulletin of Engineering Geology and The Environment,2019,78(5):3385-3394. http://doi.org/10.1007/s10064-018-1315-5

[29] Wu XH, Li P, Guo QF, et al. Research progress on the evolution of physical and mechanical properties of thermally damaged rock[J].Chinese Journal of Engineering, 2022, 44(05):827-839. https://doi.org/10.13374/j.issn2095-9389.2020.12.23.007.

[30 ]Luo J, Xiong J, Zhu MY, et al. Experimental study on the influence of temperature on rock physical properties:taking sandstone of Xujiahe formation and shale of Longmaxi formation inSichuan basin as examples[J]. Progress in Geophysics, 2023, 38(5):2080-2093. https://doi.org/10.6038/pg2023GG0376．

[31] Liu XJ, Gao H, Liang LX. Study of temperature and confining pressure effects on porosity and permeability in low permeability sandstone[J]. Chinese Journal of Rock Mechanics and Engineering, 2011, 30（S2）: 3771-3778.

[32] Amro M M, Benzagouta M S. Effect of pressure and temperature on petrophysical characteristics in the case of carbonate reservoirs[J]. Oil Gas Eur Mag, 2009, 35(29): 74-78. https://doi.org/10.2118/126045-MS.

[33] Hu YX, Ye ZY, Li S. Shear mechanical properties of rough-walled joints of red sandstone under real-time temperature[J/OL]. Journal of China Coal Society, 2024, 1-12. https://doi.org/10.13225/j.cnki.jccs.2024.0950.

[34] Zhang H ,Liu S ,Xiao H .Tribological properties of sliding quartz sand particle and shale rock contact under water and guar gum aqueous solution in hydraulic fracturing[J].Tribology International,2019,129416-426. https://doi.org/10.1016/j.triboint.2018.08.043.

[35] Chen Y. Permeability evolution of sandstone under multi-field coupling[J]. Journal of Central South University (Science and Technology), 2017, 48(9). https://doi.org/10.11817/j.issn.1672-7207.

[36] Liu Z, He X, Fan J, et al. Study on the softening mechanism and control of red-bed soft rock under seawater conditions[J]. Journal of Marine Science and Engineering, 2019, 7(7): 235. https://doi.org/10.3390/jmse7070235.

[37] Ding W, Tan S, Zhu R, et al. Study on the damage process and numerical simulation of tunnel excavation in water-rich soft rock[J]. Applied Sciences, 2021, 11(19): 8906. https://doi.org/10.3390/app11198906.

[38] Sun X, Shi F, Luan Z, et al. Constitutive model and microscopic mechanism for sandstone strength softening damage[J]. Rock Mechanics and Rock Engineering, 2023, 56(1): 797-813. https://doi.org/10.1007/s00603-022-03096-z.

[39] Li H, Zhong Z, Eshiet K I I, et al. Experimental investigation of the permeability and mechanical behaviours of chemically corroded limestone under different unloading conditions[J]. Rock Mechanics and Rock Engineering, 2020, 53: 1587-1603. https://doi.org/10.1007/s00603-019-01961-y.

[40] Peng T, Ren D, He F, et al. Study on fatigue characteristics of red sandstone under extremely high stress in the hydro-chemical environment[J]. Frontiers in Earth Science, 2024, 12: 1453080. https://doi.org/10.3389/feart.2024.1453080.

 

7.Question: Line 306, "cumulative accumulated dissipated energy," lacks clarity.

Response: Thank you for your valuable comments. I have corrected the writing errors in the text, and the modified parts are marked in red. The specific modifications are as follows:

Modification:

Modify “where  is the cumulative dissipated energy at any stress state,  is the cumulative accumulated dissipated energy of the rock, and the units of each of the above quantities are MJ·m-3. D=1 means that the rock is completely destroyed and D=0 means that the rock is intact and undamaged.” to “where  is the cumulative dissipated energy at any stress state, is the cumulative dissipation of energy consumed by rocks， and the units of each of the above quantities are MJ·m^-3. D=1 means that the rock is completely destroyed and D=0 means that the rock is intact and undamaged.

 

8.Question: You may need to clearly explain or discuss the following two questions from your data set after the heating and cooling treatment.

1.1What caused variation of physical/mechanical properties between sandstone samples?

Response: Thank you very much for the reviewer’s suggestions. The differences in the physical and mechanical properties between the sandstone samples are caused by the following two factors:

1、Temperature Effects: Different temperatures result in varying thermal expansion effects within the sandstone. At 85℃ and 95℃, the thermal expansion effects are more significant, leading to a reduction in the rock's porosity, and decreasing its permeability and water absorption. At 25℃ and 55℃, the thermal expansion effect is relatively less pronounced, promoting water infiltration and resulting in a higher water content. This phenomenon indicates that temperature changes can affect the structural properties of rocks and alter their physical properties.

2、Water Effects: The interaction between water and the mineral composition of sandstone intensifies the softening, dissolution, and stress corrosion effects on mineral particles, causing a decline in its mechanical properties. As the immersion time increases, the water content of the sandstone is highest after 3 hours. High water content exacerbates the softening and damage of the sandstone, leading to the greatest damage. Additionally, the high water content makes the mineral particles of the rock more susceptible to external forces, resulting in the generation and expansion of cracks.

The above content has been revised and reflected in the text, as shown in the red-font sections of Sections 3, 6, and 7.

 

1.2What causes the dependence of heating and cooling treatments on thermal and physical properties?

Response: Thank you very much for the reviewer’s suggestions. The dependence of the thermal and physical properties on heating treatment is caused by the following three factors:

1、Thermal Expansion Effect and Porosity Changes: Different temperatures lead to varying thermal expansion effects within the sandstone, which in turn causes changes in the internal porosity. At 85℃ and 95℃, the thermal expansion effect is more pronounced, leading to a reduction in the rock’s porosity, thereby decreasing its permeability and water absorption. At 25℃ and 55℃, the thermal expansion effect is relatively less noticeable, and the temperature promotes water infiltration, resulting in a higher water content.

2、Crack Propagation and Water Infiltration: As the temperature increases, the generation and expansion of cracks within the sandstone provide more pathways for water infiltration, increasing the water content of the sandstone. However, when the temperature reaches a certain level (85℃ and 95℃), the thermal expansion effect reduces the porosity, thus decreasing water infiltration.

3、Combined Effects of Temperature and Immersion Time: As the immersion time increases, water penetration gradually increases. At the same time, temperature enhances the thermal expansion effect of the rock, altering its pore structure. This results in the greatest damage to the sandstone at 55℃, where the crack morphology is more complex, and the rate of energy release is faster.

The above content has been revised and reflected in the text, as shown in the red-font sections of Sections 3, 6, and 7.

 

9.Question: Researchers have thoroughly investigated the effects of grain expansion during the heating process on the thermo-physical properties of sandstone. What are the effects of grain contraction during the cooling process?

Response: We greatly appreciate your review. This experiment aims to study the damage and failure patterns of sandstone under varying temperatures and immersion durations. To minimize the influence of the initial water content of the sandstone specimens on the experimental results, the selected sandstone was subjected to a drying treatment. After drying, the specimens were cooled at a rate of 0.5℃/min. During the entire process, the cooling rate did not affect the experiment, so the impact of particle shrinkage was not analyzed.

 

10.Question: Provide the mineralogical composition of the sandstone samples (after heating and cooling treatment). This would serve as solid evidence for the discussion section.

Response: We greatly appreciate your review. Prior to the experiment, we analyzed the mineral composition of the red sandstone, which consists primarily of quartz (22.7%) and feldspar (77.3%), as shown in Figure 1. According to references [1-2], under water temperatures ranging from 25℃ to 95℃, the mineral composition of sandstone (quartz and feldspar) does not change. Therefore, after heating, we did not continue to analyze the mineral composition of the red sandstone. The modified parts in the text are marked in red, and the specific modifications are as follows:

Modification:

Modify“The experimental material was sourced from sandstone in a high-temperature, water-rich tunnel in southern Tibet. The rock surface exhibited no visible cracks. X-ray diffraction analysis indicated that the primary constituents of the sandstone were quartz and feldspar.”to“The test material was selected from the sandstone inside a high-temperature, water-rich tunnel in southern Tibet. The surface of the sandstone exhibited no discernible fractures. According to diffraction composition analysis, the main components of the sandstone are quartz (22.7%) and feldspar (77.3%), as shown in Figure 1.”

[1]Sun H, Su N, Jin AB,et al.Effects of temperature on Brazilian splitting characteristics of sandstone with differentsizes[J]. Chinese Journal of Engineering, 2022,44(01):26-38. http://doi.org/10.13374/j.issn2095-9389.2021.07.26.001.

[2]Lv Q,Sun Q,Deng S,et al. Research on the Thermal Conductivity of Sandstone and Limestoneafter High Temperature Treatment[J]. Geological Journal of China Universities, 2017,23(04):626-632. http://doi.org/10.16108/j.issn1006-7493.2017027.

 

11.Question: The authors must elucidate how these findings integrate into the overarching framework of damage theory in rocks and the practical implications of their insights, particularly in geothermal applications. In what ways does this work enhance current hypotheses on rock damage due to thermal stress, and what are the ramifications for geological applications?

Response:We greatly appreciate your review. We have added a discussion section to explain how the research findings integrate into the overall framework of rock damage theory and to clarify their practical significance. The modified parts in the text are marked in red, and the specific modifications are as follows:

Modification:

6.Discussion

This study employs the WAW-1000B electro-hydraulic servo universal testing machine loading system to carry out uniaxial compression tests on sandstone samples subjected to different temperatures (25°C, 55°C, 85°C, 95°C) and soaking durations (0.5 hours, 1 hour, 3 hours). Additionally, an acoustic emission system is used to study the damage and failure characteristics of sandstone under the combined influence of temperature and water. The findings indicate that at 85°C and 95°C, the thermal expansion effect of sandstone is more evident, leading to a decrease in the rock's permeability and water absorption capacity. In contrast, at 25°C and 55°C, the thermal expansion effect of sandstone is relatively less pronounced, which promotes water infiltration and results in a higher moisture content [29-33]. High moisture content exacerbates the dissolution [34-35], softening [36-38], and stress corrosion effects [39-40] of sandstone mineral particles, causing a decline in their mechanical properties. As the soaking duration increases, sandstone samples soaked for 3 hours exhibit the highest moisture content, which intensifies their softening and damage. This results in maximum damage to the sandstone, making the mineral particles within the rock more susceptible to external forces and facilitating the initiation and propagation of cracks.）

The research results indicate that the damage to rocks in high-temperature and water-saturated environments is not solely the result of increased temperature or prolonged immersion time, but rather the result of the interaction between the two factors. This finding further reveals the damage and failure mechanisms of sandstone under the combined effects of high temperature and water, particularly the comprehensive impact of different temperatures on the thermal expansion and moisture migration of sandstone. The experiments found that 55°C is the threshold for sandstone damage, indicating that there is a turning point in the thermal expansion effect of sandstone across different temperature ranges. This means that an increase in temperature does not always uniformly affect moisture migration; instead, there are both enhancing and inhibiting effects. This finding provides a new perspective for studying the damage mechanisms of rocks in high-temperature environments and offers theoretical support for establishing more accurate rock damage models. From an engineering perspective, the research results are significant for tunnel construction in high-temperature, water-rich environments. In practical construction, special attention should be paid to the stability of surrounding rock in such temperature ranges. Measures such as optimizing drainage systems, enhancing the impermeability of surrounding rock, and implementing effective reinforcement measures can be employed to mitigate the damage to sandstone caused by high moisture content, thereby reducing the likelihood of accidents.

[29] Wu XH, Li P, Guo QF, et al. Research progress on the evolution of physical and mechanical properties of thermally damaged rock[J].Chinese Journal of Engineering, 2022, 44(05):827-839. https://doi.org/10.13374/j.issn2095-9389.2020.12.23.007.

[30 ]Luo J, Xiong J, Zhu MY, et al. Experimental study on the influence of temperature on rock physical properties:taking sandstone of Xujiahe formation and shale of Longmaxi formation inSichuan basin as examples[J]. Progress in Geophysics, 2023, 38(5):2080-2093. https://doi.org/10.6038/pg2023GG0376．

[31] Liu XJ, Gao H, Liang LX. Study of temperature and confining pressure effects on porosity and permeability in low permeability sandstone[J]. Chinese Journal of Rock Mechanics and Engineering, 2011, 30（S2）: 3771-3778.

[32] Amro M M, Benzagouta M S. Effect of pressure and temperature on petrophysical characteristics in the case of carbonate reservoirs[J]. Oil Gas Eur Mag, 2009, 35(29): 74-78. https://doi.org/10.2118/126045-MS.

[33] Hu YX, Ye ZY, Li S. Shear mechanical properties of rough-walled joints of red sandstone under real-time temperature[J/OL]. Journal of China Coal Society, 2024, 1-12. https://doi.org/10.13225/j.cnki.jccs.2024.0950.

[34] Zhang H ,Liu S ,Xiao H .Tribological properties of sliding quartz sand particle and shale rock contact under water and guar gum aqueous solution in hydraulic fracturing[J].Tribology International,2019,129416-426. https://doi.org/10.1016/j.triboint.2018.08.043.

[35] Chen Y. Permeability evolution of sandstone under multi-field coupling[J]. Journal of Central South University (Science and Technology), 2017, 48(9). https://doi.org/10.11817/j.issn.1672-7207.

[36] Liu Z, He X, Fan J, et al. Study on the softening mechanism and control of red-bed soft rock under seawater conditions[J]. Journal of Marine Science and Engineering, 2019, 7(7): 235. https://doi.org/10.3390/jmse7070235.

[37] Ding W, Tan S, Zhu R, et al. Study on the damage process and numerical simulation of tunnel excavation in water-rich soft rock[J]. Applied Sciences, 2021, 11(19): 8906. https://doi.org/10.3390/app11198906.

[38] Sun X, Shi F, Luan Z, et al. Constitutive model and microscopic mechanism for sandstone strength softening damage[J]. Rock Mechanics and Rock Engineering, 2023, 56(1): 797-813. https://doi.org/10.1007/s00603-022-03096-z.

[39] Li H, Zhong Z, Eshiet K I I, et al. Experimental investigation of the permeability and mechanical behaviours of chemically corroded limestone under different unloading conditions[J]. Rock Mechanics and Rock Engineering, 2020, 53: 1587-1603. https://doi.org/10.1007/s00603-019-01961-y.

[40] Peng T, Ren D, He F, et al. Study on fatigue characteristics of red sandstone under extremely high stress in the hydro-chemical environment[J]. Frontiers in Earth Science, 2024, 12: 1453080. https://doi.org/10.3389/feart.2024.1453080.

 

12.Question: The results are mixed with discussion. The results section presents the descriptions of the data. The discussion section provides explanations, comparisons, implications, and/or limitations based on the results.

Response:We greatly appreciate your review. Based on your suggestions, we have revised the relevant sections of the text, removing the overlap between the results and discussion. The modified parts are marked in red, and the specific changes are as follows:

Modification:

Modify“As illustrated in Figure 3, the acoustic emission signals of sandstone under different temperatures and soaking times exhibit similar patterns of change. The acoustic emission ringing and energy variations with time go through three distinct phases: ① the quiet period, ② the rapid increase period, and ③ the decay period. The cumulative ringing count of the acoustic emission increases gradually with loading time and reaches its maximum value after the peak stage. In the quiet period, due to the gradual compression of the primary pores and cracks within the sandstone, the acoustic emission signals (ringing counts, energy) of the sandstone are relatively low at all temperatures. In the rapid increase period, as the internal damage of the sandstone continues to intensify under axial force, cracks begin to develop and propagate.”to“As shown in Figure 5, at the same temperature, as the soaking time increases, the maximum AE ring count, maximum AE energy, and cumulative AE ring count of sandstone gradually decrease. When soaked for 3 hours, the acoustic emission signals (ring count, energy) and cumulative ring count of sandstone at all temperature conditions reach their minimum values. At the same soaking time, as the temperature rises, for soaking durations of 0.5 hours and 1 hour, the maximum AE ring count and maximum AE energy of sandstone exhibit a pattern characterized by an initial increase, followed by a decrease, and subsequently a further increase. In contrast, the cumulative AE ring count exhibits a gradual upward trend. For soaking durations of 3 hours at different temperatures, the maximum AE ring count, maximum energy, and cumulative AE ring count of sandstone all gradually increase with rising temperature.

With the increase in soaking time, the water content of sandstone gradually rises. High water content enhances the plastic deformation capacity of sandstone and reduces its brittleness failure degree, leading to a significant decrease in the acoustic emission signal values. This is the reason why the maximum AE ring count, maximum AE energy, and cumulative AE ring count of sandstone are all at their minimum after soaking for 3 hours. At the same soaking time but different temperatures, the water content of sandstone is highest at 55°C, resulting in weakened brittleness and enhanced plasticity of the sandstone, the sandstone exhibits a greater accumulation of energy prior to reaching the peak stress. Consequently, when failure occurs in the sandstone near the peak stress, it generates more pronounced acoustic emission signals. When the temperature further increases (above 55°C), on the one hand, the thermal expansion effect of the rock begins to appear, and on the other hand, the temperature continues to promote an increase in the water content of sandstone. The water content of the rock initially decreases and subsequently increases, resulting in a corresponding trend in the maximum ring count and maximum energy, which also exhibit a trend of first decreasing and then increasing. After soaking for 3 hours, high temperatures promote the further development of the thermal expansion effect in sandstone, causing more original microcracks to close, thereby significantly increasing the ring count and energy of the acoustic emission signals [23].”

 

13.Question: The conclusion and abstract should undergo a revision. Write the content and the numerical values; improve the conclusion and abstract section by incorporating the significant thermal-physical changes at different temperatures due to associated thermal cracking (discussed in the discussion section).

Following references is very helpful how to estimate thermal property from mineral composition.

1. Gautam, P. K., Singh, S. P., Agarwal, A., & Singh, T. N. (2022). Thermomechanical characterization of two Jalore granites with different grain sizes for India’s HLW disposal. Bulletin of Engineering Geology and the Environment, 81(11), 1-26.
2. Sirdesai, N. N., Gupta, T., Singh, T. N., & Ranjith, P. G. (2018). Studying the acoustic emission response of an Indian monumental sandstone under varying temperatures and strains. Construction and Building Materials, 168, 346-361.

Response: We greatly appreciate your review. We have revised the abstract and conclusion, and analyzed the provided references. In the abstract and conclusion sections, we have added specific details and values related to the significant thermophysical changes in sandstone at different temperatures due to thermal cracking (which have already been discussed in the discussion section).

The modified parts in the text are marked in red, and the specific changes are as follows:

Modification:

Abstract:In modern tunnel construction, complex environments with high geothermal gradients and abundant groundwater are frequently encountered. To investigate the damage and failure mechanisms of sandstone under the combined effects of temperature and water, uniaxial compression tests were conducted on sandstone at different temperatures (25°C, 55°C, 85°C, and 95°C) and soaking durations (0.5 h, 1 h, 3 h). The acoustic emission (AE) signals and energy evolution during the damage and failure processes were analyzed, revealing the damage characteristics and failure mechanisms of sandstone. The results indicate the following:（1）As the temperature increases, under the 3-hour condition, the water content of sandstone is highest at 55°C, reaching 3.01%, and the thermal expansion effect of sandstone is not obvious. Under the conditions of 85°C and 95°C, the thermal expansion effect leads to a decrease in the water content, enhances the water absorption softening effect, increases the plastic deformation capacity of sandstone, and weakens its brittle failure capacity. （2）When soaked for 0.5 h and 1 h, the maximum acoustic emission ring count and maximum acoustic emission energy of sandstone increase initially, then decrease, and subsequently increase again as the temperature rises, while the cumulative acoustic emission ring count gradually increases with temperature. Under the 3-hour soaking condition, the maximum ring count, maximum energy, and cumulative ring count of sandstone at all temperatures show a consistent increasing trend with temperature. （3）The increase in soaking time reduced the damage variable of sandstone, with the largest reduction of 54.17% under the 3-hour condition. At different temperatures, the damage variable of sandstone was smallest at 55°C, only 0.33 （4）Sandstone primarily experiences tensile failure under different temperatures and soaking times. The extension of soaking time promotes the development of shear cracks, while the increase in temperature can effectively promote the expansion of tensile cracks. The research results provide certain theoretical references for the damage and failure of surrounding rock in modern tunnel construction.

1. Introduction

Currently, numerous scholars have conducted extensive research on the damage mechanisms and failure characteristics of rocks under the effects of temperature, water, or their combined effect. Sirdesai et al. [1] conducted uniaxial compression tests on sandstone at temperatures ranging from 200°C to 1000°C and found that the expansion of mineral grains and anisotropy lead to changes in the physical and mechanical properties of the sandstone.

6. Dicussion

This study employs the WAW-1000B electro-hydraulic servo universal testing machine loading system to carry out uniaxial compression tests on sandstone samples subjected to different temperatures (25°C, 55°C, 85°C, 95°C) and soaking durations (0.5 hours, 1 hour, 3 hours). Additionally, an acoustic emission system is used to study the damage and failure characteristics of sandstone under the combined influence of temperature and water. The findings indicate that at 85°C and 95°C, the thermal expansion effect of sandstone is more evident, leading to a decrease in the rock's permeability and water absorption capacity. In contrast, at 25°C and 55°C, the thermal expansion effect of sandstone is relatively less pronounced, which promotes water infiltration and results in a higher moisture content [29-33]. High moisture content exacerbates the dissolution [34-35], softening [36-38], and stress corrosion effects [39-40] of sandstone mineral particles, causing a decline in their mechanical properties. As the soaking duration increases, sandstone samples soaked for 3 hours exhibit the highest moisture content, which intensifies their softening and damage. This results in maximum damage to the sandstone, making the mineral particles within the rock more susceptible to external forces and facilitating the initiation and propagation of cracks.

The research results indicate that the damage to rocks in high-temperature and water-saturated environments is not solely the result of increased temperature or prolonged immersion time, but rather the result of the interaction between the two factors. This finding further reveals the damage and failure mechanisms of sandstone under the combined effects of high temperature and water, particularly the comprehensive impact of different temperatures on the thermal expansion and moisture migration of sandstone. The experiments found that 55°C is the threshold for sandstone damage, indicating that there is a turning point in the thermal expansion effect of sandstone across different temperature ranges. This means that an increase in temperature does not always uniformly affect moisture migration; instead, there are both enhancing and inhibiting effects. This finding provides a new perspective for studying the damage mechanisms of rocks in high-temperature environments and offers theoretical support for establishing more accurate rock damage models. From an engineering perspective, the research results are significant for tunnel construction in high-temperature, water-rich environments. In practical construction, special attention should be paid to the stability of surrounding rock in such temperature ranges. Measures such as optimizing drainage systems, enhancing the impermeability of surrounding rock, and implementing effective reinforcement measures can be employed to mitigate the damage to sandstone caused by high moisture content, thereby reducing the likelihood of accidents.

7.Conclusion

Through uniaxial compression tests conducted on sandstone under different temperatures and soaking times (with varying moisture content), the damage characteristics and failure mechanisms of sandstone were investigated. The following conclusions were drawn.

（1）Different temperatures and soaking durations can influence the thermal expansion effect of sandstone. Under the condition of 3 hours, the moisture content of sandstone is highest at 55°C, and the thermal expansion effect of sandstone is not significant. At 85°C and 95°C, the moisture content decreases, and the water absorption softening effect increases.

（2）Under the influence of different soaking durations and temperatures, the acoustic emission of sandstone undergoes a period of calm, a surge, and a decay. At different temperatures, for soaking durations of 0.5 hours and 1 hour, the maximum ringing, energy, and cumulative ringing count of acoustic emission from sandstone exhibit a trend of initially increasing, followed by a decrease, and then increasing again. However, for a soaking duration of 3 hours, the maximum ringing, energy, and cumulative ringing count of acoustic emission gradually increase as the temperature rises.

（3）Under varying soaking durations and temperature conditions, sandstone exhibits the lowest total energy, elastic energy, total energy absorption rate, and elastic energy absorption rate at 55°C. Conversely, it shows the highest pre-peak dissipated energy and dissipated energy release rate at this temperature. Among different temperatures, the damage variable of sandstone is the largest at 55°C.

（4）The RA parameter of acoustic emission indicates that sandstone mainly undergoes tensile failure. An increase in temperature can effectively promote the development of tensile cracks, while an increase in soaking duration can facilitate the development of shear cracks, but tensile failure remains the dominant failure mode.

[1] Gautam P K, Singh S P, Agarwal A, et al. Thermomechanical characterization of two Jalore granites with different grain sizes for India 's HLW disposal[J]. Bulletin of engineering geology and the environment, 2022, 81(11): 1-26. http://doi.org/10.1007/s10064-022-02962-y.

[2] Sirdesai N N, Gupta T, Singh T N, et al. Studying the acoustic emission response of an Indian monumental sandstone under varying temperatures and strains[J]. Construction and Building Materials, 2018, 168: 346-361. http://doi.org/10.1016/j.conbuildmat.2018.02.180.

[3] Pan P Z, Shao C Y. Experimental studies on the physical and mechanical properties of heated rock by air, water and high-viscosity fluid cooling[J]. Geomechanics for Energy and the Environment, 2022, 31: 100315. http://doi.org/10.1016/j.gete.2022.100315.

[4] Cai C, Wang B, Zou Z, et al. Experimental Study on the Damage and Failure Characteristics of High-Temperature Granite after Liquid-Nitrogen Cooling[J]. Processes, 2023, 11(6): http://doi.org/1818. 10.3390/pr11061818.

[5] Cui Y, Xue L, Zhai M, et al. Experimental investigation on the influence on mechanical properties and acoustic emission characteristics of granite after heating and water-cooling cycles[J]. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 2023, 9(1): http://doi.org/88.10.1007/s40948-023-00627-y.

[6] Hu X, Hong B, Meng Y. Statistical damage model of red sandstone with effect of water ratio considered[J]. JOURNAL-CHINA UNIVERSITY OF MINING AND TECHNOLOGY-CHINESE EDITION-, 2007, 36(5): 609.

[7] Azhar M U, Zhou H, Yang F, et al. Water-induced softening behavior of clay-rich sandstone in Lanzhou Water Supply Project, China[J]. Journal of Rock Mechanics and Geotechnical Engineering, 2020, 12(3): 557-570.http://doi.org/10.1016/j.jrmge.2019.07.017.

[8] Wasantha P L P, Ranjith P G, Permata G, et al. Damage evolution and deformation behaviour of dry and saturated sandstones: insights gleaned from optical measurements[J]. Measurement, 2018, 130: 8-17. http://doi.org/10.1016/j.measurement.2018.07.075.

[9] Alomari E M, Ng K W, Khatri L, et al. Effect of Physical Properties on Mechanical Behaviors of Sandstone under Uniaxial and Triaxial Compressions[J]. Materials, 2023, 16(13): 4867. http://doi.org/10.3390/ma16134867.

[10] Zhao Y, Liu J, Zhang C, et al. Mechanical behavior of sandstone during post-peak cyclic loading and unloading under hydromechanical coupling[J]. International Journal of Mining Science and Technology, 2023, 33(8): 927-947. http://doi.org/10.1016/j.ijmst.2023.05.004.

[11] Guha Roy D, Singh T N, Kodikara J, et al. Effect of water saturation on the fracture and mechanical properties of sedimentary rocks[J]. Rock Mechanics and Rock Engineering, 2017, 50: 2585-2600. http://doi.org/10.1007/s00603-017-1253-8

[12] Ping Q, Gao Q, Wang C. Mechanical test study on thermo-water coupled dynamic splitting of annular sandstone specimens with different inner diameters[J]. Journal of Vibration and Shock, 2023, 42(17): 43-51+152. http://doi.org/10.13465/j.cnki.jvs.2023.17.006

[13] Yan MH. Physical and Mechanical Properties of Thermal-liquid-stress Coupled Granite[D]. Baoding: Hebei University,2020. http://doi.org/10.27103/d.cnki.ghebu.2020.001218.

[14] Yang F,Wang G,Hu D,et al. Influence of water-rock interaction on permeability and heat conductivity of granite under high temperature and pressure conditions[J]. Geothermics, 2022, 100： 102347. http://doi.org/10.1016/j.geothermics.2022.102347.

[15] Wang C, Hu MG, Wang C. Dynamic damage characteristics and structural model of concentric perforated granite subjected to thermal-hydro-mechanical coupling[J]. Rock and Soil Mechanics, 2023, 44(03): 741-756.

[16] Zheng C,Yao Q,Li X, et al. Experimental investigation of mechanical characteristics of coal samples at different drying temperatures[J]. Drying Technology,2022,40(16)：3483-3495. http://doi.org/10.16285/j.rsm.2022.0887.

 

[29] Wu XH, Li P, Guo QF, et al. Research progress on the evolution of physical and mechanical properties of thermally damaged rock[J].Chinese Journal of Engineering, 2022, 44(05):827-839. https://doi.org/10.13374/j.issn2095-9389.2020.12.23.007.

[30 ]Luo J, Xiong J, Zhu MY, et al. Experimental study on the influence of temperature on rock physical properties:taking sandstone of Xujiahe formation and shale of Longmaxi formation inSichuan basin as examples[J]. Progress in Geophysics, 2023, 38(5):2080-2093. https://doi.org/10.6038/pg2023GG0376．

[31] Liu XJ, Gao H, Liang LX. Study of temperature and confining pressure effects on porosity and permeability in low permeability sandstone[J]. Chinese Journal of Rock Mechanics and Engineering, 2011, 30（S2）: 3771-3778.

[32] Amro M M, Benzagouta M S. Effect of pressure and temperature on petrophysical characteristics in the case of carbonate reservoirs[J]. Oil Gas Eur Mag, 2009, 35(29): 74-78. https://doi.org/10.2118/126045-MS.

[33] Hu YX, Ye ZY, Li S. Shear mechanical properties of rough-walled joints of red sandstone under real-time temperature[J/OL]. Journal of China Coal Society, 2024, 1-12. https://doi.org/10.13225/j.cnki.jccs.2024.0950.

[34] Zhang H ,Liu S ,Xiao H .Tribological properties of sliding quartz sand particle and shale rock contact under water and guar gum aqueous solution in hydraulic fracturing[J].Tribology International,2019,129416-426. https://doi.org/10.1016/j.triboint.2018.08.043.

[35] Chen Y. Permeability evolution of sandstone under multi-field coupling[J]. Journal of Central South University (Science and Technology), 2017, 48(9). https://doi.org/10.11817/j.issn.1672-7207.

[36] Liu Z, He X, Fan J, et al. Study on the softening mechanism and control of red-bed soft rock under seawater conditions[J]. Journal of Marine Science and Engineering, 2019, 7(7): 235. https://doi.org/10.3390/jmse7070235.

[37] Ding W, Tan S, Zhu R, et al. Study on the damage process and numerical simulation of tunnel excavation in water-rich soft rock[J]. Applied Sciences, 2021, 11(19): 8906. https://doi.org/10.3390/app11198906.

[38] Sun X, Shi F, Luan Z, et al. Constitutive model and microscopic mechanism for sandstone strength softening damage[J]. Rock Mechanics and Rock Engineering, 2023, 56(1): 797-813. https://doi.org/10.1007/s00603-022-03096-z.

[39] Li H, Zhong Z, Eshiet K I I, et al. Experimental investigation of the permeability and mechanical behaviours of chemically corroded limestone under different unloading conditions[J]. Rock Mechanics and Rock Engineering, 2020, 53: 1587-1603. https://doi.org/10.1007/s00603-019-01961-y.

[40] Peng T, Ren D, He F, et al. Study on fatigue characteristics of red sandstone under extremely high stress in the hydro-chemical environment[J]. Frontiers in Earth Science, 2024, 12: 1453080. https://doi.org/10.3389/feart.2024.1453080.

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors corrected the manuscript according to the recommendation. I accept the manuscript in its present form.

Reviewer 2 Report

Comments and Suggestions for Authors

NA

Comments on the Quality of English Language

NA