Embankment Displacement PLAXIS Simulation and Microstructural Behavior of Treated-Coal Gangue
Round 1
Reviewer 1 Report
In this paper the authors used FEM to simulate the filling stage and solidification process of coal gangue embankment. Although the topic of this research is of interest of engineers, there are some major issues that should be addressed before publication.
The authors should modify the title of this paper. It is interpreted from the title that the microstructural properties of the coal gangue are simulated in this paper using PLAXIS. This is not true since the simulation of microstructural characteristics of the coal gangue cannot be simulated in PLAXIS unless the authors incorporate the microstructural properties of the material in the software. In this paper, the coal gangue is treated as a homogeneous material (using MC constitutive model), therefore the title of the paper should be modified to prevent any misinterpretations. In additions, she authors investigated the microstructure of the samples in the laboratory which cannot be explicitly simulated in the software. The authors should give an explanation that how change in the microstructural properties of the material influences its overall mechanical response (e.g. Young’s modulus etc.). The construction of the model in PLAXIS is questioned. The authors mentioned that the sand layer below the clay layer is non-deformable (Line 117). However, the interface between sand and clay layer may affects the overall behaviour of the numerical model. The authors should clarify this issue and provide a reason that why simulation of the sand-clay interface is not necessary here. From Figure 1, it can be observed that the interface between subgrade CG and clay is explicitly simulated in PLAXIS software. However, the authors did not mention how the mechanical properties of this interface is introduced in the numerical model. Obviously, the shear failure of this interface promotes the overall failure of the slope leading to instability of the structure. Thus, it is necessary to provide enough data about the CG-clay interface and select an interface model in PLAXIS (if any) to simulate the mechanical behaviour of the CG-clay interface correctly. The authors should clarify how they applied the in-situ stress condition in their numerical model. Without, introducing the in-situ stress condition, which is an essential boundary condition in numerical modelling, the outcomes will not be reliable, therefore any interpretation of the numerical results will be inaccurate. The authors mentioned different stages to complete the numerical analysis. After stage 2 (200 days) the 3 m of coal layer is consolidated, and its mechanical properties are different from the new coal gangue layer. Firstly, the authors should explain how the difference between the mechanical properties of old and new coal gangue layers is introduced in the model. Secondly, explain if the simulate of interface between the new and the old coal gangue layer is necessary or not. Line 157: the authors referred to maximum horizontal and vertical displacements. However, in Figure 3, only vertical displacement of the model is provided. Please clarify this issue. Section 3.3: The authors should explain how the water condition is simulated in the numerical model. Whiteout providing the necessary explanations, it would be impractical to interpret the numerical outcomes depicted in Figure 4. Section 4: In this section, only the results of laboratory investigation are provided. Thus, these analyses should be differentiated from the numerical simulation results in the title of this paper.Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper studies on the displacement of the embankment using different treated-coal gangue through PLAXIS simulation. The author conducted some microstructural tests to explain the behavior and results of FEM simulation. Reading the whole story of the paper, the reviewers a few major comments and some minor comments as below:
Major comments:
“The main chemical composition (presented in Table 1) of coal gangue was determined by X-raydiffraction spectrometry (XRD) according to ASTM: E 1621-05”.How can we use XRD for determining the chemical compositions of coal gangue? In general, XRD can be used to determine the minerals of materials.
“The CG was crushed, screened, and selected assamples with sizes between 9.5 and 16 mm”.Why we have to crush samples to that size?
“Coal gangue is easily to react with acid and alkali, socommonly used treatment solutions are hydrochloric acid, sulfuric acid, nitric acid, acetic acid,sodium hydroxide, potassium hydroxide, and calcium hydroxide”.How it reacts and what kind of reaction occurs in this case?
How is the concentration of acid and alkaline solution for the mixture? “In order to allow the specimen to react completely with the solutions, coal gangue was soaked inAcetic Acid (A-CG), Tap Water (T-CG) and Sodium Hydroxide (S-CG) for 15 days”.How can the authors know that 15 days, coal gangue will react completely and what is the definition of complete reaction here?
Line: 80: “CG and solutions were prepared by solid-liquid ratio (mass ratio) of1:1”. How are the preparation and curing conditions of each mixture? What age and how can the author determine the five parameters of clay as well as A-CG, T-CG, and S-CG in table 5? “In order to ensure the stability of the coal gangue subgrade, when the filling heightis 8 m, the slope rate should not be steeper than 1:1.5”.Why the author did not calculate the stability of the embankment (safety factor of slope stability)? Although the author calculates the displacement of Slope Toe, it is better to calculate the safety factor of slope.
Line 120-121: what is the minimum pore pressure? Because the authors show results of Ultra-Static Pore Water Pressure but the reviewer did not see the underground water table; so, what is ultra-static pore water pressure? How is the level of underground water? “All the treated samples at each stage in Table 3 have a smaller vertical displacement value thanthe untreated Raw-CG”. Why, please add the discussion “All the treated samples at each stage in Table 3 have a smaller vertical displacement value thanthe untreated Raw-CG”. Please add the discussion or reason. “Inthe fourth stage, with long-term solidification, the ultra-static water pressure in the Raw-CGspecimen is distributed in the lower subgrade and near the clay, and its value is greater than the otherthree specimens”. Why did this phenomenon happen? Please add the discussion. Line 163: “while the displacements of samples untreated and treated by alkaline solution arecomparatively large”. What is the reason for this large displacement by alkaline treatment? Line 258-263: “S-CG subgradedisplacement is the largest, because the alkali solution is easier to enter the inside of the coal gangueglass body, OH- can break the surface Al-O, Si-O network [45], Na-Si-Al gel formed around the coalgangue particles, the other material in the coal gangue is difficult to escape, so that the sample hashigh viscosity and density, but its settling displacement is smaller and the solidification effect is betterthan that of untreated coal gangue material”.
The reviewer may not agree with this explanation because looking at Table 2, we can see S-CG produce a higher density as well as cohesion (c), and it can produce Na-Si-Al à the displacement could not be larger than T-CG.
The author used SEM and EDS Spectrum Analysis and Raman Spectrum Analysis to explain the behavior of each material before and after treatment. However, these tests only conducted for the specimens at 15 days after treatment; thus, it is difficult to simulate the behavior of the analysis in PLAXIS after 200 days or more. As the author knows, for a long time some other reactions will occur, thus new products produced and could change the microstructure of this material.
Minor comments:
The authors used some technical words and phrases may be not common or wrong. The paper must be checked by a native speaker.
soft land foundation à soft soil foundation?
sticky land base? à cohesive soil base?
ultra-static water pressure à excess pore water pressure?
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors responded to the comments appropriately, however there is still concerns about the simulation of interfaces in the PLAXIS software. The authors provided the maximum shear stress in response to comment No. 4 without indicating the zone(s) in which the shear stress is measured. In addition, the mechanical properties of the interfaces should be incorporated in the numerical model in order to achieve a reliable numerical outcome. It is necessary to clearly demonstrate the constitutive relationships of the interface model and its mechanical properties in the paper. Also, an explanation should be added to the manuscript describing how the interface model’s parameters are chosen in this numerical research.
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
The revised version significantly improved and addressed all comments of the reviewer.
Thank you very much.
Author Response
Dear reviewer, we appreciate for your valuable comments on our paper. We have checked English spell, improved methods description, experiment results, conclusions.
Round 3
Reviewer 1 Report
The responses provided by the authors are satisfactory, and the numerical outputs are interesting. The manuscript can be published now without additional revisions.
