Research on the Long-Term Mechanical Behavior and Constitutive Model of Cemented Tailings Backfill Under Dynamic Triaxial Loading

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review report for the manuscript titled:

Research on the Long-Term Mechanical Behavior and Constitutive Model of CTB Under Dynamic Triaxial Loading

This article addresses an important topic, which is the study of the long-term mechanical properties of cemented tailings backfill (CTB) under dynamic triaxial loading. This topic is of particular importance due to the use of CTB in mine backfill applications, especially in environments with dynamic and deep conditions. The researchers in this study used a sophisticated experimental system to conduct triaxial compression tests, focusing on the effect of different pressures and loading and unloading methods on the behavior of the material. The researchers also sought to build a mathematical constitutive model to describe this behavior, which represents a valuable addition to this field.

Abstract:

The current abstract is generally good, providing an accurate summary of the study objectives, methodology, and main findings. However, there are some aspects that could be improved to make the abstract clearer and more comprehensive.

1- It may be useful to add a sentence or two at the beginning of the abstract to explain the importance of CTB in mine backfilling operations, and an overview of the challenges it faces in dynamic conditions, justifying the need for this study.

2- The abstract refers to the construction of the constitutive model, but does not provide any details about the nature of the model (such as the type of equation or variables used). It might be helpful to add a sentence explaining the nature of the model in general.

3- The abstract does not mention any limitations of the study, such as the range of stresses tested, the types of materials used, or the assumptions made. It is always a good idea for the abstract to mention some limitations of the study to be more transparent.

1- Introduction:

Ø  The introduction starts well by identifying the main problem, which is the increasing challenges in deep mining. Mentioning challenges such as “high ground pressure, high temperatures, rock instability, and rockfall hazards” puts the reader in the context of the problem and justifies the need to explore innovative solutions. However, this section could be enhanced by providing more detail on the challenges mentioned. For example, specific examples of rockfalls that have occurred in deep mines could be cited, or statistics could be provided to illustrate how dangerous high ground pressure is. This would make the problem more tangible. I therefore recommend adding specific examples and statistical data to support the claims about the challenges of deep mining.

Ø  The introduction correctly emphasizes the importance of the mechanical properties of CTB, which is an essential or even permanent part of the mine structure. The connection between the stability of CTB, the control of mining site pressure, and the maintenance of long-term stability of the mine structure highlights the importance of the research. However, the importance of these properties could be further explained. For example, it could be mentioned how the pressure generated by the CTB affects the stability of the mine, or how the weakness of the CTB can lead to structural problems. Consequently, I suggest including a section that explains the direct connection between the mine's long-term stability and the mechanical characteristics of CTB.

Ø  The introduction states that the research focuses on “the mechanical properties of CTB under triaxial dynamic conditions”. This is a good point, as it highlights that there is a gap in previous studies that have not sufficiently focused on this aspect. However, this gap can be further elaborated. What types of dynamic conditions have not been sufficiently studied? Is it cyclic loading? Is it vibration?  Defining this precisely will make the research gap clearer.

Ø  The authors did not mention in the introduction the type of filling material used specifically (ultrafine cemented tailings backfill) although it was mentioned in the abstract. The type of filling material used should be mentioned in the introduction so that there is consistency between the abstract and the introduction in this regard.

 

2. Materials and Schemes

2.1. Experimental Materials

Ø  This section delineates the materials utilized in the experiment, which is crucial for comprehending the study's methodology. The primary components of the packing material (CTB) utilized in the study are identified as "ultrafine tailings from a gold mine," a laboratory-made cementing material, and water. While "ultrafine tailings from a gold mine" is referenced, additional details are necessary. From which gold mine? Were any pretreatments used to the tailings? These details will facilitate a deeper comprehension of the material employed.

Ø  Despite its seeming simplicity, it is advisable to mention the type of water utilized (e.g., distilled water, tap water). Any water treatment, such as desalination, should be explicitly mentioned.

Ø  It is preferable that the text indicates that the exact quantities of materials used in the experiment will be mentioned later (e.g. in the experimental methodology section). This gives the reader a clearer idea of ​​how the test samples were prepared.

2.2. Experimental Scheme

2.2.1. Specimen Preparation

The current section is good at providing a basic description of the sample preparation process, but it needs more detail in several aspects to ensure repeatability of experiments and accuracy of results. By adding some details to enhance this section significantly as follows:

Ø  Detail the mixing process accurately (type of mixer, mixing time, mixing speed(.

Ø  Determine the exact proportion of water used (water to cement ratio).

Ø  Detail the grinding process (type of grinding machine, finishing criteria).

Ø  Justify the time specified for demoulding.

Ø  State the homogeneity criterion used to ensure homogeneity of the mixture.

Ø  State the number of samples prepared for each experiment.

2.2.2. Experimental Scheme

This section provides a good description of the experimental plan in general but needs more detail in some aspects to ensure clarity of methodology and repeatability of the experiments.

Ø  The subheading (2.2.2) must be unique and sufficiently detailed to distinguish its content from the main section (2.2). both are “Experimental Scheme”

Ø  The units used must be standardized. For example, when the loading rate is mentioned once in mm/s and once in mm/min, these units must be standardized so that the research is consistent.

Ø  Initial loading: The text states that σ1 was loaded to 0.5 MPa, then σ₂ to 0.7 MPa, then σ₃ to 0.5 MPa. Why were these values ​​chosen specifically? What is the justification for this order of loading?

Ø  The text states that σ1 is loaded to 80% of the triaxial compressive strength. How was this strength determined? Was it based on previous experiments? What is the rationale for using 80% specifically?

Ø  Was each experiment repeated multiple times? If so, how many times? The number of repetitions is important to assess the accuracy of the results.

Ø  Were the measuring devices/machines used calibrated before conducting the experiments?

3. Results and Analyses

3.1. Study on Mechanical Properties of Backfill Under Static True Triaxial Compression

3.1.1. Stress-Strain Curve Analysis

Ø  The authors relied primarily on the stress-strain curve in the Results section, however, there is a lack of detail about how the strain was measured in the Materials and Schemes section above, and this information is essential for assessing the accuracy of the results and for the possibility of replicating the experiments by other researchers. Were strain gauges or displacement transducers used? The authors should explain the method used to measure the strain, including the type of sensors used (strain gauges or displacement transducers), how they were installed, and how the data were corrected for any possible errors.

3.1.2. Analysis of Acoustic Emission Characteristics

The text states that figure 7 represents sound emission under different intermediate principal stresses, but does not explain in detail how the intermediate stress affects these stages. Does the intermediate stress affect the duration of each stage? Or the signal intensity? Or the cumulative energy? An analysis of this effect should be added.

4. Construction of Constitutive Model

Ø  What does it mean for the damage to be isotropic? Does this mean that the damage is distributed evenly in all directions? Is this assumption valid for CTB?

Ø  Why was the Weibull distribution chosen? Is there a scientific rationale for selecting this distribution? What are the attributes of this distribution?

The researchers state that ‘some studies have shown that the Weibull distribution is the most appropriate for describing the statistical distribution of CTB’ [11]. This statement is not specific and needs further clarification. Please cite specific studies that support this claim, and explain why the Weibull distribution is more appropriate than other distributions. The ref. [11] may not be sufficient to support this claim.

If these recommendations are implemented, the paper will be ready for publication and enhances our fundamental understanding of the complex failure mechanisms and long-term stability of CTB materials in deep mining environments.

v Recommendation:

Based on the above comments, my recommendation is [accepted with major revisions].

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Introduction

In the introduction, there are several passages that cite other studies addressing triaxial tests, but they do not go in-depth. That is, they do not highlight what these studies concluded or how these conclusions relate to supporting the analyses of the current study being presented. To illustrate, here is one of the passages that contains this flaw, which should be corrected:

“Rong et al. analyzed the deformation and failure characteristics of deep rock under different stress paths and the evolution law of mechanical parameters by carrying out true triaxial experiments of rock under different stress paths [18-21]. Miao et al. studied the energy evolution of rock under cyclic loading and unloading and discussed the relationship between energy dissipation and rock strength [22,23]. Lu et al. studied the mechanical properties of the backfill-rock composite structure under triaxial compression conditions, and analyzed the failure mechanism of the backfill rock composite structure [24].”

The following passage has already been mentioned in the first paragraph of the introduction (lines 67–68) and should be removed.

At present, domestic and foreign scholars have done a lot of research on the acoustic emission characteristics of rock under uniaxial and triaxial compression conditions.

What are the conclusions of the studies cited in the following passage (lines 69-74)?

Long et al. usaram um teste de carregamento cíclico multinível, combinado com monitoramento de emissão acústica e varredura de TC pós-teste. Os efeitos da relação cimento-rejeitos no desempenho de fadiga, atividade de emissão acústica, dissipação de energia e modo de fratura de amostras de estrutura composta de aterro de rocha circundante foram estudados [29]. Gao et al. realizaram testes de compressão triaxial e emissão acústica em massa rochosa, revelando o processo de deformação e fratura e as características de emissão acústica da massa rochosa [30].

Materials and Schemes

Why was the 1:4 ratio used for sample preparation? (line 120)

The experimental methodology is very well detailed, congratulations! However, it is important to justify the choices of the stresses adopted for the different tested schemes, as well as the velocities.

Despite a detailed experimental approach, the range of tested conditions could be expanded to include different mining environments, variations in material composition, and other factors that could affect CTB performance. It is essential that these limitations be addressed in the text.

Results

The captions of figures 7, 8, 9, 10, 11, 12, 13, and 14, “MPa” is written incorrectly

The analysis of the results (item 3) was based solely on the experiments conducted, from the mechanical and acoustic tests. There is no correlation of the results or foundation for the analyses in previous studies, that is, other published works. In addition to describing what is observed in the graphs, it is necessary to relate it to what already exists in the literature.

Although the study is relevant to mining engineering, it does not discuss how its findings can be practically implemented in real mining operations. The article does not consider the impact of environmental factors such as temperature and humidity on the resistance of the material studied, which could be relevant for application in different mining scenarios.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The paper is technically correct but of low interest for the readers. It looks like a lab report with strangely looking section with the constitutive model which is not supported by any calculation or simulation.  There is nothing new in sample preparation, testing methodology and data analysis. Actually, there is a lack of aggregation of the results in a bigger picture. There is also lack in in-deep analysis. For instance, in the section “Study on Long-Term Mechanical Properties of Backfill Under Bidirectional Disturbance” I do not find anything related to creep and rate effects – typical phenomenon for long-term mechanical behavior.

Maybe I not the right person to find nuances and details that are novel, but rough search in google scholar reveals many very similar research, even in true triaxial tests apparatus.

To conclude, there is lack of in-deep analysis, the topic is not novel, the data are not aggregated into one bigger picture and the constitutive model is added ad-hoc without any explanations and verification.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I appreciate you taking the time to consider every feedback and recommendation from the first review carefully. I value the changes made to the manuscript to make it more accurate and clear. I have no more serious issues because the paper has been greatly strengthened. Since it now satisfies the quality requirements, I suggest publishing this version.

Reviewer 2 Report

Comments and Suggestions for Authors

After the revisions, the article appears to be suitable for publication.