Excavation construction stability evaluation method for super-large-section subway station based on core rock pillar reinforcing method

Abstract

The invention provides an ultra-large section subway station excavation construction stability evaluation method based on a core rock pillar reinforcing method. The method comprises the following steps that a numerical model of a tunnel is established; analyzing the state of the core rock pillar before excavation, and judging whether the core rock pillar is in a stable state at the moment; arranging a middle partition wall for the core rock pillar and comparing and selecting reinforcement measures of the core rock pillar; the plurality of monitoring points are used for analyzing the influence of the reinforcement measures on the stability of the core rock pillar by analyzing the displacement characteristics of the monitoring points in the tunnel excavation process; a judgment matrix is formed, then the maximum characteristic value is calculated, and finally consistency check is carried out to obtain a weight; and performing fuzzy comprehensive evaluation on the set reinforcement measures to obtain an optimal reinforcement measure. According to the method, the mechanical behavior of a core rock pillar is analyzed, three reinforcing measures are provided, three different supporting working conditions are designed, results of the three working conditions are analyzed and compared, all the supporting working conditions are comprehensively evaluated through an analytic hierarchy process, and the optimal reinforcing measure is determined.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, and in particular to a method for evaluating the excavation construction stability of a super-large-section subway station based on a core rock column reinforcement method. Background Art

[0002] As a key measure to ease traffic congestion, subway construction has attracted much attention for its construction safety and efficiency. The ultra-large cross-section tunnel and the complex geology and surrounding environment pose severe challenges to construction technology. In particular, during the tunnel excavation process, the stability of the core rock column of the upper step is directly related to the success or failure of the entire project. How to reinforce the core rock column to ensure its stability is a key issue.

[0003] In the existing technology, there is insufficient research on the core rock pillars of ultra-large cross-section tunnels, and no evaluation of reinforcement measures; for tunnels with ultra-large cross-sections and high construction difficulty, ensuring the stability of the core rock pillars under the ultra-large cross-section is a key issue; how to comprehensively evaluate various support conditions and determine the optimal reinforcement measures is an urgent problem that needs to be solved. Summary of the invention

[0004] In view of this, the problem to be solved by the present invention is to provide a stability assessment method for the excavation construction of a super-large section subway station based on the core rock column reinforcement method. This method analyzes the mechanical behavior of the core rock column, proposes three reinforcement measures, designs three different support conditions, analyzes and compares the results of the three conditions, and comprehensively evaluates each support condition through the hierarchical analysis method to determine the optimal reinforcement measure.

[0005] The present invention solves the above technical problems by the following technical means: The present invention provides a method for evaluating the stability of excavation construction of a super-large-section subway station based on a core rock column reinforcement method, comprising the following steps:

[0006] Establish a numerical model of the tunnel based on the project cross-sectional area, station length and geological conditions;

[0007] Performing a state analysis of the core rock column before excavation according to the numerical model, and determining whether the core rock column is in a stable state before excavating the core rock column;

[0008] Setting up intermediate walls for core rock columns and comparing and selecting reinforcement measures;

[0009] The Y=s section of the tunnel numerical model is selected as the investigation section, and several monitoring points are set on the investigation section. The influence of reinforcement measures on the stability of the core rock column is analyzed by analyzing the displacement characteristics of the monitoring points during the tunnel excavation process.

[0010] The displacement of the monitoring point is used as the evaluation index, the importance of each evaluation index is judged, a judgment matrix is ​​constructed, and then the maximum eigenvalue is calculated. Finally, a consistency test is performed to obtain the weight;

[0011] According to the weight values ​​of the determined monitoring points, the reinforcement measures are fuzzy comprehensively evaluated to obtain the optimal reinforcement measures.

[0012] Furthermore, the mesh of the numerical model adopts quadrilateral units, and lateral displacement constraints are added to the left and right sides of the model, and vertical displacement constraints are applied to the bottom side of the model.

[0013] Furthermore, the distribution thickness of the rock and soil in the numerical model is determined according to the geological longitudinal section of the tunnel. Except for the core rock and soil, the other initial support parameters adopt grid arch frame + system anchor rod + mesh shotcrete. The initial support uses a three-dimensional shell unit, the steel arch frame and shotcrete are simplified into one, and the elastic modulus of the steel arch frame is converted into concrete.

[0014] Furthermore, the reinforcement measures for the core rock column include: improving the strength of the surrounding rock itself; increasing the restraint force on the core rock column by setting up temporary support; using tension anchor rods to strengthen the restraint force on the core rock column by applying prestress to the anchor rods.

[0015] Furthermore, the method also includes calculating the eigenvector, weight value, maximum eigenroot and CI value of the judgment matrix by using MATLAB program, and performing consistency test.

[0016] Furthermore, the fuzzy comprehensive evaluation of the set reinforcement measures also includes inverse processing of the data of key points, and then fuzzy averaging of the inverse processed data to obtain membership calculation results, and then comparing the membership calculation results obtained from different reinforcement measures to obtain the optimal reinforcement measures.

[0017] It can be seen from the above technical scheme that the beneficial effects of the present invention are as follows: the present invention provides a method for evaluating the excavation construction stability of a super-large section subway station based on a core rock column reinforcement method, comprising the following steps: establishing a numerical model of a tunnel according to the engineering section area, the station length and the geological conditions; analyzing the state of the core rock column before excavation according to the numerical model, and judging whether the core rock column is in a stable state before excavating the core rock column; setting a middle partition wall for the core rock column and comparing its reinforcement measures; selecting the Y=s position section of the numerical model of the tunnel as the investigation section, setting a number of monitoring points on the investigation section, and analyzing the influence of the reinforcement measures on the stability of the core rock column by analyzing the displacement characteristics of the monitoring points during the tunnel excavation process; using the displacement of the monitoring point as an evaluation index, judging the importance of each evaluation index, forming a judgment matrix, and then calculating the maximum eigenvalue, and finally performing a consistency test to obtain the weight; performing a fuzzy comprehensive evaluation on the set reinforcement measures according to the determined weight value of the monitoring point, and obtaining the optimal reinforcement measures. This method analyzes the mechanical behavior of the core rock column, proposes three reinforcement measures, designs three different support conditions, analyzes and compares the results of the three conditions, and uses the hierarchical analysis method to comprehensively evaluate each support condition to determine the optimal reinforcement measure. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0019] Figure 1 A step diagram of a method for evaluating the excavation construction stability of a super-large-section subway station based on a core rock column reinforcement method provided by the present invention;

[0020] Figure 2 This is the standard cross-section diagram of Section A of the tunnel;

[0021] Figure 3 This is a schematic diagram of the two-dimensional model of the tunnel;

[0022] Figure 4 This is a schematic diagram of the three-dimensional model of the tunnel;

[0023] Figure 5 This is the horizontal deformation diagram of the middle partition rock column;

[0024] Figure 6 It is the horizontal stress distribution diagram of the middle partition rock column;

[0025] Figures 7 to 9 The following are the reinforcement measures schematic diagrams for the three working conditions 1, 2 and 3 respectively;

[0026] Figures 10-12 The vertical displacement cloud diagrams of the three working conditions are as follows:

[0027] Figures 13-15 The horizontal convergence cloud diagrams of the three working conditions are as follows: working condition 1, 2, and 3;

[0028] Figures 16-17 It is the displacement map of 4 key points;

[0029] Fig.18 Schematic diagram of membership results of different reinforcement measures. DETAILED DESCRIPTION

[0030] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

[0031] For example, see Figures 1 to 18 The present invention provides a method for evaluating the stability of excavation construction of a super-large-section subway station based on a core rock column reinforcement method, comprising the following steps:

[0032] A numerical model of the tunnel is established according to the cross-sectional area of ​​the project, the length of the station and the geological conditions; the mesh of the numerical model adopts quadrilateral units, and lateral displacement constraints are added to the left and right sides of the model, and vertical displacement constraints are applied to the bottom side of the model;

[0033] Specifically, Figures 2 to 4 As shown in the figure, the numerical model is established based on the actual cross-sectional area, station length and geological conditions of the actual project. In order to eliminate the influence of boundary effects, the horizontal width of the model is 160m, the length is 170m, and the height is 85m. The tunnel excavation width B = 26.14m, the excavation height s = 22.14m, the overburden depth is 24m, and the model is modeled according to the actual original overburden thickness of the geological survey. The modeling results are shown in the figure. Figure 2 As shown in the figure, lateral displacement constraints are added to the left and right sides of the model, and vertical displacement constraints are applied to the bottom. The model grid uses quadrilateral units, and the calculation unit is divided into 1m.

[0034] Performing a state analysis of the core rock column before excavation according to the numerical model, and determining whether the core rock column is in a stable state before excavating the core rock column;

[0035] Specifically, the distribution thickness of the rock and soil mass is taken according to the geological longitudinal section of the tunnel, including 5m of artificial fill and 80m of sandy mudstone. Except for the core rock column, the other initial support parameters adopt grid arch frame + system anchor + mesh shotcrete. The initial support uses a three-dimensional shell unit (ssell), the steel arch frame and shotcrete are simplified into one, and the elastic modulus of the steel arch frame is converted into concrete. The physical parameters of the rock and soil mass are obtained through on-site engineering tests, and the remaining material parameters are obtained according to the actual engineering design. The physical parameter values ​​of the specific tunnel rock and soil mass, lining structure and temporary support are shown in Table 1.

[0036] Table 1 Physical and mechanical parameters of materials

[0037]

[0038] Setting a middle partition for the core rock column and comparing its reinforcement measures; the reinforcement measures for the core rock column include: improving the strength of the surrounding rock itself; increasing the restraint force on the core rock column by setting temporary support; using tension anchor rods to strengthen the restraint force on the core rock column by applying prestress to the anchor rods;

[0039] Specifically, before excavating the core rock column, it is necessary to first analyze whether the core rock column is in a stable state. Figure 5 As shown by Figure 5 It can be seen that the core rock column has been extruded into the pit due to the unloading disturbance of the pilot pit excavation on the left and right sides, and the maximum horizontal deformation is about 2.02mm. In terms of stress, since the vertical stress remains basically unchanged, and the horizontal stress is unloaded due to excavation, the shear stress of the core rock column increases, so that its stress state will approach the failure state line, and the stability of the middle partition rock column will decrease, but it is still in a stable state. However, since the surrounding rock generally has rheological properties, its deformation will continue to increase over time under the stress stability state, so the vault settlement will continue to develop, further reducing the stability of the core rock column. Although the calculation results show that the core rock column is in a stable state, due to the rheological characteristics of the surrounding rock, the stability of the core rock column may gradually decrease. Therefore, in order to ensure the excavation stability, it is necessary to set the middle partition of the core rock column and compare its support measures.

[0040] There are generally three options for strengthening the core rock column. The first condition is to improve the strength of the surrounding rock itself, such as using grouting and mortar anchors. The second condition is to increase the restraint on the core rock column by setting up temporary support. The third condition is to use tension anchors to strengthen the restraint on the core rock column by applying prestress to the anchors. Under weak surrounding rock conditions, the deformation of the surrounding rock is large, and the application of tension anchors will produce a large prestress loss; the use of grouting anchors can effectively improve the stability of the surrounding rock.

[0041] The middle partition wall is 10.22m high and 5.65m wide. In order to ensure the stability of the core rock column and the timely implementation of the initial support of the vault, reasonable and effective reinforcement measures must be selected to enhance the bearing capacity of the core rock column and improve its stability. It is necessary to analyze different auxiliary supports and reinforcement measures while constructing the left and right guide holes by the step method to ensure the stability of the core rock column. Therefore, it is necessary to analyze the different forms of several reinforcement measures in Table 2 to obtain a better reinforcement method for the core rock column. The schematic diagram of the three reinforcement measures is shown in Figure 2. Figures 7 to 9 shown.

[0042] Table 2 Core rock column reinforcement measures

[0043]

[0044] The Y=s section of the tunnel numerical model is selected as the investigation section, and several monitoring points are set on the investigation section. The influence of reinforcement measures on the stability of the core rock column is analyzed by analyzing the displacement characteristics of the monitoring points during the tunnel excavation process.

[0045] Specifically, the Y=10m section of the tunnel model is selected as the investigation section to analyze the vault settlement and horizontal convergence of the tunnel. A total of 4 key points are set, namely S1, S2, S3, and S4. Figure 2 The displacement characteristics of key points during tunnel excavation are analyzed to analyze the impact of reinforcement measures on the stability of the core rock column.

[0046] pass Figures 10-12 It can be seen that the overall deformation of the tunnel is symmetrically distributed along the tunnel axis, with the maximum settlement occurring at the arch and the maximum uplift occurring at the bottom mid-span, and the uplift deformation being greater than the settlement deformation. The settlement in working condition 1 is the largest because only anchor bolts are driven into the core rock column, which can reinforce the surrounding rock, but its effect is limited.

[0047] pass Figures 13-15 It can be seen that based on working condition 1, working condition 2 added a steel frame as a temporary support, and the maximum settlement was significantly reduced, indicating that the temporary support can effectively bear the vertical load above the core rock column, reduce settlement, and improve the stability of the core rock column. In addition, in the process of excavating the core rock column, the core rock column is removed after its deformation is stabilized, which can further ensure the safety of the tunnel excavation process. The settlement of working condition 3 is the smallest, and the settlement is further reduced after the locking anchor is driven in, because when the locking anchor is applied, part of the pressure of the surrounding rock will be transmitted to the lower rock mass through the anchor.

[0048] According to Table 3 and Figures 13-15It can also be seen that the key points S1 and S2 are also consistent with the above analysis, while the key points S3 and S4 reflect the horizontal convergence of the core rock column. After the left and right guide tunnels were excavated successively, the left and right sides of the core rock column lost support and deformed outward, and the horizontal convergence of the right side was lower than that of the left side. This is because the left guide tunnel was excavated first, which produced a larger disturbance first, and the excavation depth was greater than that of the right guide tunnel. After the steel frame and locking anchor rods were applied, the horizontal deformation of the core rock column was limited, and the horizontal displacements of S3 and S4 were gradually reduced under the three working conditions.

[0049] Table 3 Displacement of key points in three working conditions of section Y=10m

[0050]

[0051] Therefore, the middle partition wall, as a temporary supporting structure, can bear part of the surrounding rock pressure and transfer stress, and reduce the stress state of the core rock column. The middle partition wall divides the upper step into three parts for excavation, effectively separates the excavation surface, reduces the single excavation area, and thus reduces the disturbance and damage to the surrounding rock. Secondly, adding locking anchor rods can lock the ends of the steel arch frame, increase the contact between the steel arch frame and the surrounding rock, fully bear the deformation pressure of the surrounding rock, and constrain the longitudinal and vertical deformation of the steel arch frame. In addition, the locking anchor rods have a good restraining ability on the deformation of the surrounding rock vault. Therefore, adding locking anchor rods and middle partition walls can effectively reduce the settlement and horizontal convergence of the tunnel vault, which helps to improve the excavation stability.

[0052] The displacement of the monitoring point is used as the evaluation index, the importance of each evaluation index is judged, a judgment matrix is ​​constructed, and then the maximum eigenvalue is calculated. Finally, a consistency test is performed to obtain the weight;

[0053] Specifically, the displacement of the four key points monitored is used as the evaluation index, the importance of each evaluation index is judged, a judgment matrix is ​​constructed, and then the maximum eigenvalue is calculated, and finally a consistency test is performed to obtain the weight. The construction of the judgment matrix can use the scaling method (see Table 4) to compare the importance of each index pairwise and construct a judgment matrix.

[0054] Table 4 Judgment matrix for pairwise comparison of indicators

[0055]

[0056] According to Table 4, a judgment matrix can be constructed. The judgment matrix of the four indicators is presented in the form of a table, as shown in Table 5.

[0057] Table 5 Key point index judgment matrix

[0058]

[0059] According to the weight value of the determined monitoring point, the reinforcement measures set are fuzzy comprehensively evaluated to obtain the optimal reinforcement measures. The data of the key points are inversely processed, and then the inversely processed data are fuzzy averaged to obtain the membership calculation results, and then the membership calculation results obtained by different reinforcement measures are compared to obtain the optimal reinforcement measures.

[0060] Specifically, the MATLAB program is used to calculate the eigenvector, weight value, maximum eigenroot and CI value of the judgment matrix, and to perform consistency test. The calculation results are shown in Tables 6 and 7.

[0061] From Tables 6 and 7, we can see that the weight of the right horizontal convergence S4 is 6.776%, the weight of the left horizontal convergence S3 is 9.583%, the weight of the bottom uplift S2 is 30.615%, and the weight of the arch settlement S1 is 53.026%. The maximum characteristic root is 4.215, and the corresponding RI value is 0.882 according to the RI table. Therefore, CR = CI / RI = 0.081 < 0.1, passing the one-time test.

[0062] Table 6 AsP hierarchical analysis results

[0063]

[0064] Table 7 Consistency test results

[0065]

[0066] According to the weight values ​​of the four key points, the three working conditions are fuzzy comprehensively evaluated to obtain the optimal reinforcement measures. First, the data of the key points are reversed. Since the displacement of the surrounding rock is a negative indicator, the larger the indicator, the worse it is, which is not convenient for comparison. Therefore, it is convenient for comparison after reversing it. The data in Table 3 in the previous article are reversed as shown in Table 8. The data in Table 8 are fuzzy evaluated and processed. Fig.18 Membership calculation results.

[0067] Table 8 Displacement inversion data under different reinforcement measures

[0068]

[0069] according to Fig.18 It can be seen that the membership degree of working condition 3 is 0.54, the membership degree of working condition 2 is 0.46, and the membership degree of working condition 1 is 0. Working condition 3> working condition 2> working condition 1, so the support scheme of working condition 3 is considered to be the optimal reinforcement measure.

[0070] Among them, the AsP method is used to construct the index system and calculate the weight of each index, which is specifically divided into the following three steps: (1) Select indicators to build a hierarchical structure; (2) Construct a pairwise comparison judgment matrix A based on the importance scale; (3) Perform a consistency test on the judgment matrix and calculate the weight of each factor;

[0071]

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A method for evaluating the stability of excavation construction of a metro station with a large cross section based on a core rock column reinforcement method, characterized in that: The steps include: Establish a numerical model of the tunnel based on the project cross-sectional area, station length and geological conditions; Performing a state analysis of the core rock column before excavation according to the numerical model, and determining whether the core rock column is in a stable state before excavating the core rock column; Setting up intermediate walls for core rock columns and comparing and selecting reinforcement measures; The Y=s section of the tunnel numerical model is selected as the investigation section, and several monitoring points are set on the investigation section. The influence of reinforcement measures on the stability of the core rock column is analyzed by analyzing the displacement characteristics of the monitoring points during the tunnel excavation process. The displacement of the monitoring point is used as the evaluation index, the importance of each evaluation index is judged, a judgment matrix is ​​constructed, and then the maximum eigenvalue is calculated. Finally, a consistency test is performed to obtain the weight; According to the weight values ​​of the determined monitoring points, the reinforcement measures are fuzzy comprehensively evaluated to obtain the optimal reinforcement measures.

2. The method for evaluating the stability of excavation construction of a metro station with a large cross section based on the core rock column reinforcement method according to claim 1 is characterized in that: The mesh of the numerical model adopts quadrilateral units, and lateral displacement constraints are added to the left and right sides of the model, and vertical displacement constraints are applied to the bottom side of the model.

3. The method for evaluating the stability of excavation construction of a metro station with a large cross section based on the core rock column reinforcement method according to claim 2 is characterized in that: The distribution thickness of the rock and soil in the numerical model is determined according to the geological longitudinal section of the tunnel. Except for the core rock and soil, the other initial support parameters adopt grid arch frame + system anchor rod + mesh shotcrete. The initial support uses a three-dimensional shell unit, the steel arch frame and shotcrete are simplified into one, and the elastic modulus of the steel arch frame is converted into concrete.

4. The method for evaluating the stability of excavation construction of a metro station with a large cross section based on the core rock column reinforcement method according to claim 1 is characterized in that: The reinforcement measures for the core rock column include: improving the strength of the surrounding rock itself; increasing the restraint force on the core rock column by setting up temporary supports; using tension anchor rods to strengthen the restraint force on the core rock column by applying prestress to the anchor rods.

5. The method for evaluating the stability of excavation construction of a metro station with a large cross section based on the core rock column reinforcement method according to claim 1 is characterized in that: It also includes using MATLAB program to calculate the eigenvector, weight value, maximum eigenroot and CI value of the judgment matrix, and performing consistency test.

6. The method for evaluating the stability of excavation construction of a metro station with a super-large cross-section based on the core rock column reinforcement method according to claim 5 is characterized in that: The fuzzy comprehensive evaluation of the set reinforcement measures also includes inverse processing of the data of key points, and then fuzzy averaging of the inversely processed data to obtain membership calculation results, and then comparing the membership calculation results obtained from different reinforcement measures to obtain the optimal reinforcement measures.

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