Application of Numerical Simulation Technology in New Intelligent Reinforcing Method of Shield Tunnel End in Seaside Environment
Round 1
Reviewer 1 Report
The paper "Application of Numerical Simulation Technology in New Intelligent Reinforcing Method of Shield Tunnel End in Seaside Environment" presents the research achievements ensuring the smooth start and arrival of the shield machine in the domestic subway construction and avoiding engineering accidents such as instability of the end soil, surface subsidence, and landslide. The authors use a coupling framework of GIS and SWMM model, and the use of GIS technology to extract parameters required by the model.
The paper is of good quality. There are, however, a few grammatical errors. See some examples of them in the followings.
lines 38-39: Shield method is an advanced, efficient and safe construction method.
missing article and comma
The Shield method is an advanced, efficient, and safe construction method.
line 80:shield tunneling method
the shield tunneling method
line 83:with poor self-stabilization ability
with a poor self-stabilization ability
line 89:analyse
analize
line 96: definition of thin plate
missing article
line 96: dimension of thin plate
missing article
line 98:Practice has proved that, ignoring some ...
unnecessary comma
line 204:water-stop
line 210:waterstop
Please choose one form.
Figures 3-5. σ1-σ3
σ1-σ3 are not noted in the figure, so it is strange to refere to them.
Author Response
The grammatical errors in the text have been corrected according to the suggestions.
Reviewer 2 Report
(1) It is difficult to read because there are too many paragraphs.
(2) It is difficult to know the contribution of the paper because the problem definition is not clear.
(3) There is no precise specification of the experimental design and experimental analysis method, and '3. Results and Discussion' comes right out of the background explanation, so I don't understand the thesis.
(4) It is difficult to identify novelty and contribution as it is not a new theory or equation established, but a paper that specifies the results of experiments in compliance with existing theories.
(5) It seems to be a simple background listing without investigating related studies and specifying limitations.
Author Response
- I have deleted some paragraphs and restructured the article.
- The instability of the soil at the shield end is an important safety hazard in the shield tunnel construction. In loose and weak strata, the risk of instability and damage is higher and the loss is greater. In this paper, the instability and failure of the end soil in loose and weak strata are studied. In order to ensure the smooth departure and arrival of the shield and avoid engineering accidents such as end soil instability, surface subsidence, landslide, etc. during the construction process, this paper summarizes the commonly used reinforcement technology and characteristics of the shield in and out of the tunnel, and through the combination of indoor model test and numerical model test, studies the failure mechanism of the PFC end upper body in soft and loose strata, and calculates the reinforcement stability coefficient.
- The numerical calculation software used in this paper is PLAXIS 3D. The model size used in the finite element analysis is the same as the corresponding test size, which is 1.1m × 0.9m × 1.2m. The finite element software PLAXIS3D uses the function of material data group to divide the functional attributes of each soil layer and structure into different categories for construction: soil and interface, geogrid, beam, plate, anchor rod and embedded pile. When defining soil parameters, you need to enter the data group of soil and interface, select the constitutive model of soil and fill in the corresponding data to get the soil model.
According to the construction sequence and stratum loss unloading in the actual test, the test process of simulating shield tunnel end reinforcement is divided into 9 steps, and the construction stage is defined in the PLAXIS 3D distributed construction interface. The specific steps are as follows:
(1) Initial phase: the stress field of the whole model is in equilibrium by generating initial stress; (2) Tunnel placement: freeze the soil above the tunnel top buried depth, and simulate the excavation process before placing the tunnel; Then activate the plate element of the tunnel model and activate the corresponding forward interface, which simulates the process of placing the tunnel model; (3) Generate pile group foundation: activate the frozen soil at the upper part, activate the pile group foundation and positive interface, and simulate the construction of pile group. In order to prevent the activation of the pile foundation structure from changing the original stress state of the soil and causing the displacement of the soil, the displacement of this step is reset to zero; (4) Simulate the formation loss: activate the surface shrinkage of the model tunnel slab unit, and set the value of the surface shrinkage to simulate the formation loss process of tunnel excavation.
- In this paper, the portal is reinforced before the shield machine enters the portal; the principle, scope and method of soil reinforcement at the end of working shaft are analyzed; the strength of reinforced soil is analyzed by the theory of plate strength; the stability of reinforced soil is analyzed by slip instability theory; design, inspect and control the construction process of soil reinforcement of end wells.
- The literature review has been added.
Reviewer 3 Report
Comments: I have carefully reviewed the paper and found that the results of the paper look interesting Overall, the paper and subject are related to the journal's scope and are interesting topic for the readers. Therefore, the manuscript can be accepted for publication after the major revisions.
1. The abstract must be improved by providing an overview of some of the important outcomes.
2. The introduction should be answering the following questions.
a) What is the problem?
b) Why it is hard to follow?
c) Why it has been selected?
d) What efforts have been made previously?
e) What were the drawbacks of the previously developed techniques?
f) What is the novelty of this work?
g) In addition, the author can take help from Soil Dynamics and Earthquake Engineering, 163, 107499, Journal of Structural Engineering, 149(1), 4022222. Journal of Composites for Construction, 27(2), 4023007. Appl. Opt., 61(21), 6330-6338. Computers & Structures, 279, 106970. Complex & Intelligent Systems. doi: 10.1007/s40747-022-00910-7, Engineering Structures, 279, 115619. doi: 10.1109/TNNLS.2021.3054611, Computer-aided civil and infrastructure engineering, 36(11).
3. The numbering of the equations in the manuscript is not presented in a scientific way. So I suggest the authors extensively read the manuscript and such mistakes should be removed in the revised version.
4. Following my previous comment, punctuation should be followed in the mathematical equations.
5. Results are satisfying and have been clearly presented but I would suggest adding the practical meaning of the graphs.
Author Response
- Through numerical simulation, the influence of the thickness of the added solid on the formation and diaphragm wall is analyzed. It is found that the reinforcement effect increases with the increase of the thickness of the added solid, but the change rate becomes smaller and smaller. The physical and mechanical properties of loose sand and soft clay are ob-tained through the indoor triaxial test, and the biaxial compression numerical model is established using PFC2D, and the wall constraint type is improved. With the help of PFC biaxial test, the in-fluence of model parameters on the macroscopic properties of the simulated material was analyzed. The research has certain reference value for the actual construction of the project.
- The introduction has been supplemented accordingly.
a. In this paper, the instability and failure of the end soil in loose and weak strata are studied.
b. The instability of the soil at the shield end is an important safety hazard in the shield tunnel construction. In loose and weak strata, the risk of instability and damage is higher and the loss is greater.
c. If the surrounding environment of the shield tunnel is of soil with a poor self-stabilization ability and strong water permeability, if the reinforcement treatment is not carried out in time, it is likely to collapse, causing the surface to sink and endangering nearby buildings and underground pipelines.
d. According to the different methods to prevent the collapse of the excavation face and the destruction of the enclosure structure of the tunnel portal, the current shield tunnel end shaft construction mainly includes the self-stabilizing method of cutting face and the directly exhausting the well wall method.
e. The cost of these two construction methods is relatively high, so they are rarely used in domestic shield construction. For departure and arrival operations, any of the above-mentioned construction methods can be used alone, or a combination of them can be used.
f. In this paper, the portal is reinforced before the shield machine enters the portal; the principle, scope and method of soil reinforcement at the end of working shaft are analyzed; the strength of reinforced soil is analyzed by the theory of plate strength; the stability of reinforced soil is analyzed by slip instability theory; design, inspect and control the construction process of soil reinforcement of end wells.
g. Thank you for your recommendation.
3. The number of equations in the manuscript has been adjusted.
4. After checking, I have confirmed there is no need to use punctuation in the mathematical equation.
5. In order to fit the graphs with the article, I have revised the title of Figure 1.
Reviewer 4 Report
The author studied the instability and failure of the end soil of the shield in soft stratum during shield tunnel construction, which provided theoretical and experimental proof for the smooth start-up and arrival of the shield. But the content of the paper has some defects, hope the following suggestions can be helpful to the improvement of the paper:
(1)When using abbreviations for the first time, write down the full name first.
(2)Where the GIS and SWMM models in the abstract are reflected in the text.
(3)The content of line 67 is repeated.
(4)Lines 88-92 only state the research methods and principles, not the main purpose.
(5)In Section 2.1, how is it understood to regard elastic sheets as a small combustion problem?
(6) In line 105, the previous sentence mentioned that the calculation results will be biased, how to ensure that there will be no problems in the construction?
(7)What do the parts in Figure 1- Figure 2 represent?
(8)What is the main purpose of line 129? Complete the main purpose.
(9)Carefully examine the content, such as lines 144, 170, 282, 308, 327-329, 379, 386, 399.
(10)In line 159, the research object is divided into cohesive soil and what other types of soil?
(11)The last paragraph of section 2.2 is very abstract and can be described by adding pictures.
(12) What is the formula on line 221?
(13)As mentioned in the first paragraph of Section 3.3, the assumption is quite different from the reality. How to prove the correctness of the simplification.
(14)The first conclusion in Section 5 is that the experimental process is not a conclusion.
(15)The research contribution mentioned in line 415 is not only this point, should be appropriately supplemented.
Author Response
The author studied the instability and failure of the end soil of the shield in soft stratum during shield tunnel construction, which provided theoretical and experimental proof for the smooth start-up and arrival of the shield. But the content of the paper has some defects, hope the following suggestions can be helpful to the improvement of the paper:
(1)When using abbreviations for the first time, write down the full name first.
Reply
The abbreviation has been completed.
(2)Where the GIS and SWMM models in the abstract are reflected in the text.
Reply
I have modified the abstract according to the main content.
(3)The content of line 67 is repeated.
Reply
There are two main methods of directly excavating the well wall, namely the NOMST (Novel Material Shield-cuttable Tunnel-Wall System) construction method and the EW (Electricity-erode Wall) construction method [9].
(4)Lines 88-92 only state the research methods and principles, not the main purpose.
Reply
During the construction, it is necessary to avoid the instability of the stratum caused by the long exposure time of the excavation surface, and minimize the impact on the soil when the enclosure structure is removed and the shield machine passes through the soil at the end, so as to ensure the safety of shield construction.
(5)In Section 2.1, how is it understood to regard elastic sheets as a small combustion problem?
Reply
For rectangular thin plates with different boundary conditions, the theoretical solution can be obtained by superposing the bending moment of the boundary with the solution of simply supported rectangular thin plates on four sides. Therefore, according to the actual situation of engineering construction and the relevant knowledge of plate and shell theory, the simple supported rectangular small deflection thin plate is used to simulate the reinforcement of soil, and the load on the plate is mainly the lateral pressure of soil distributed in trapezoid. The formula for calculating the maximum bending stress and shear stress of the reinforced soil mass is obtained by using the Levy Solution. Applying the calculation formula of the maximum bending stress and shear stress of the reinforced soil to engineering practice can check whether the strength of the reinforced soil meets the safety requirements.
(6) In line 105, the previous sentence mentioned that the calculation results will be biased, how to ensure that there will be no problems in the construction?
Reply
Such research and calculation results are partial to safety for the end reinforcement of thick plate, and there will be no engineering problems or accidents.
(7)What do the parts in Figure 1- Figure 2 represent?
Reply
According to the basic knowledge of plate theory of elastic mechanics, it is assumed that the diameter of the end reinforcement soil is D. According to the basic knowledge of soil mechanics, the circular thin plate is subjected to hydrostatic pressure and lateral earth pressure, and the combined force of the two is trapezoidal load. The trapezoidal load acting on a circular section is an asymmetric problem, and the mathematical model is quite complex. It is very difficult to obtain an accurate solution that satisfies all the basic equations and boundary conditions. In previous mechanical models, the trapezoidal load is simplified to uniformly distributed load, and then the axial symmetry knowledge of elastic mechanics is used to obtain the longitudinal reinforcement range that meets the strength criteria, as shown in Figure 1.
Because the result of the solution after the trapezoidal load is simplified to uniformly distributed load is dangerous. In view of this, through the analysis and research of traditional mechanical models, the advantages and disadvantages of traditional research methods are summarized, and the equivalent mechanical model is established within the allowable range of elasticity. According to Figure 2, the trapezoidal load is equivalent to the superposition of uniformly distributed load and triangular symmetric load, that is, the superposition of solving a symmetric problem.
(8)What is the main purpose of line 129? Complete the main purpose.
Reply
I have revised it to "Common problems in China's end soil reinforcement" and added the content.
(9)Carefully examine the content, such as lines 144, 170, 282, 308, 327-329, 379, 386, 399.
Reply
All the above problems have been checked and corrected.
(10)In line 159, the research object is divided into cohesive soil and what other types of soil?
Reply
According to whether the soil has cohesion, it is divided into cohesive soil and sandy soil, and two different mechanical models are established respectively.
(11)The last paragraph of section 2.2 is very abstract and can be described by adding pictures.
Reply
In view of relevance, this paragraph has been deleted.
(12) What is the formula on line 221?
Reply
L2=2*3*B
(13)As mentioned in the first paragraph of Section 3.3, the assumption is quite different from the reality. How to prove the correctness of the simplification.
Reply
To prove the correctness of the simplification of the reinforced end soil, the finite element analysis technology can be used to calculate the reinforced end soil, and the results can be compared with the actual situation. In addition, experimental methods can also be used to verify the simplified results.
(14)The first conclusion in Section 5 is that the experimental process is not a conclusion.
Reply
It has been modified to: The indoor triaxial test shows that the flexible wall not only makes the boundary conditions closer to the actual test, but also saves the traditional wall servo and calculation time.
(15)The research contribution mentioned in line 415 is not only this point, should be appropriately supplemented.
Reply
The authors extend their appreciation to the characteristic innovation (Natural Science) projects of scientific research platforms and scientific research projects in Guangdong Universities in 2021 for funding this research work through the project number (2021KTSCX139).
Round 2
Reviewer 2 Report
It seems to be sufficient for the paper to be published.
Reviewer 3 Report
Accepted.
Reviewer 4 Report
Good!
