Fluid-Solid Coupling Effect on Numerical Simulation of Deep Foundation Pit Deformation in Soft Soil Area

Round 1

Reviewer 1 Report

This study explores the deformation mechanism under the coupled fluid-solid action of foundation pits in soft soil areas. In addition, the author Combined with flow network diagram to analyze the principle of the influence of aquitard and waterproof curtain on deformation, which has a certain practical value.

The paper is well-organized and mainly written in a simple and clear language, so it is easy for readers to follow. There are a few points that I want to mention and the paper can be published after the revisions mentioned are made.

1.      “Fluid-solid coupling” is more accurate than “fluid-structure coupling” in the article and title.In addition,the modeling method of regional foundation pit seepage model mentioned in the abstract is not clearly reflected below.

2.      Abstract and Introduction. What is the definition of “soft soil area” and why focus on “soft soil area”, this needs to be explained.

3.      The engineering background in page 2，only the depth of excavation is mentioned, but there is no horizontal width and length of the pit, so there is no way to make accurate reference to it.Still in the engineering context, it is mentioned that the y-axis is the axis of symmetry, but the y-direction is defined differently in different articles, and this has to be defined precisely.

4.      In the mechanical parameters of the soil in Table 1 on page 3, the first and second layers of soil are both filled soil, but the properties are the same except the depth and thickness are different, so why should these two be separated out separately. In addition, the units under the shear-experiment are written in a confusing way and need to be corrected.

5.      Line 121-122.Based on Biot consolidation theory, the basis for adoption and the basic assumptions of Biot consolidation theory should be further explained.

6.      The article simply mentions the formula based on Biot consolidation theory, and does not list its initial conditions and boundary conditions. It is not clear whether the boundary conditions set are consistent with the chosen pit, and whether the pit is surrounded by a permeable or impermeable layer is not mentioned.

7.      Page 4 equations (2) to (4) only show the equations, how the subsequent calculations and the results of the calculations need to be given further, and how to use in this article also needs to be further explained. In addition, its equations (2) to (4) are given in the flow-solid coupling equation, so it is necessary to give the equation calculation for non-flow-solid coupling in the article.

8.      Line 126-129.Need to explain how the simulation or parameter setting for the waterproof curtain in the numerical calculation.

9.      Line 142-144.the maximum displacement calculated by the fluid-solid coupling model is -20.1mm, which appears at the burial depth of -11.4m; the maximum value calculated by the non-fluid-solid model is 14.9mm, which appears at the burial depth of -10.4m. However, it can be seen from Figure 2 that the fluid-solid coupling model is represented by a dashed line, and the maximum lateral displacement does not exceed -15mm, and the non-fluid-solid coupling model is also inconsistent, and the whole conclusion is contrary to the legend.

10.  Line 142-148. What “non-fluid- structure coupling” refers to and how it differs from “fluid- structure coupling”, this should be explained clearly.The condition settings for the fluid-solid coupling model and non-fluid-solid coupling model experiments are not clear.

11.  The correspondence between the fluid-solid model and the non-fluidsolid model is wrong, and it is impossible to conclude that the fluid-solid coupled model is in better agreement with the actual monitoring data, and the maximum displacement calculated by the fluid-solid coupled model is closer to the actual value. The description of the whole section 3.1 is confusing and wrong.

12.  Line 151-152.the experiments show that the simulation results based on the von Mises yield criterion are closer to the experimental values. However, this von Mises yield criterion is not even mentioned earlier in section 3.2 of the article. How this yield criterion is derived and how it is said to be more consistent with this experimental value requires some data or figure examples to be provided as a basis.

13.  Line 154-156.the von Mises stress distribution pattern of the fluid-solid coupling model is similar to that of the non-fluid-solid coupling model. However, it is clear from Fig. 4 that the two trends are relatively the same, but the maximum stress difference at the same depth is very different, what causes it and whether it can still be generalized as similar.

14.  Line 166. 242.9 kPa,which occurs at a depth of -1.9m burial. The depth of the mutation point is the setting depth of the support structure. Should the setting depth of the support structure be stated in advance.

15.  Line 173. “In the air” means “inside the pit” or “in the air”. Please make further explanation.

16.  Based on the Figure. 7 . Need for connotation and interpretation of flow network diagrams in Chapter 3. What do the arrows mean and should be described.

17.  Line 236-239. Why the permeability coefficient of impermeable layers increases or decreases exponentially and the basis for the selection of parameters. Please make further explanation.

18.  Line 242-244.The results of the study show that:the increase of the permeability coefficient of the weakly permeable layer leads to the increase of the horizontal displacement and the decrease of the surface settlement. However, the fourth paragraph mentions that this is the reason why the horizontal displacement of bored pile increases with the decrease of permeability coefficient. The preceding and following paragraphs are contradictory, logically confusing, and inconsistent with Figure 9.

19.  Line 268-271.The description of Figure 13 through Figure 16 is incorrect and does not match the order of the figures; Figures 15, 16 should come before and Figures 13, 14 should come after.

20.  The references were too less, especially for international journal.

Author Response

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Reviewer 2 Report

the authors used COMSOL Multiphysics to model the layers of the foundation pits and establish a two-dimensional seepage-consolidation coupled model for hierarchical dewatering excavation based on the monitoring of deep foundation pits with waterproof curtains in Shanghai deep foundation pits.

The work done looks interesting to the field, however, the authors should address the following:

1. The authors have to explain in details based on what they have decided on the meshing distribution in the problem at hand.

2. Comsol is used in this work which is a commerically available software and based low order finite element method. In this regard, and for a better accuracy, the authors should point in the introduction section that spectral element method can be emplyed due to its ultimate accuarcy. they may refer to https://opg.optica.org/josab/abstract.cfm?uri=josab-33-4-656 

3. more discussion must be included to explain the differences between figure 7 and figure 8

4. the authors have to clearly state enough justification about the choice of the practical parameters required to sovle the problem

Author Response

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