Method for determining support interval of circular shield tunnel excavation face in water-rich stratum

Abstract

This invention discloses a method for determining the support zone of the excavation face of a circular shield tunnel in water-rich strata, comprising the following steps: S1, using finite difference numerical simulation technology to simulate the groundwater seepage process during shield tunnel construction, and constructing a numerical analysis model of groundwater seepage in a shield tunnel in water-rich strata; S2, running the numerical analysis model of groundwater seepage in a shield tunnel in water-rich strata until the groundwater seepage stabilizes; S3, extracting the node coordinates and corresponding pore water pressure values ​​within the study area under the stable groundwater seepage state. The beneficial effects are: combining finite difference numerical simulation technology and the upper limit theory of limit analysis to construct a calculation model of the safe zone of the excavation face of a circular shield tunnel in water-rich strata, the safe zone of the excavation face of a circular shield tunnel in water-rich strata can be obtained more efficiently and accurately; controlling the actual support pressure according to the calculated safe support zone can effectively control the stability of the excavation face and surface settlement, providing a reliable guarantee for the construction safety of shield tunnels in water-rich strata.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering, specifically to a method for determining the support section of the excavation face of a circular shield tunnel in water-rich strata. Background Technology

[0002] In recent years, with the accelerated pace of urbanization in my country, urban subway tunnels inevitably need to be excavated in water-rich strata. Due to their advantages such as high safety, high efficiency, and minimal impact on surface structures, shield tunneling machines are highly favored in tunnel construction. During shield tunneling in water-rich strata, the continuous support pressure provided by the shield machine to the excavation face needs to balance not only the soil pressure behind the excavation face but also the additional pore water pressure generated by the presence of groundwater; that is, it needs to balance the water and soil pressure behind the excavation face.

[0003] When the support pressure applied by the tunnel boring machine (TBM) to the excavation face is insufficient to balance the water and soil pressure behind the excavation face, the soil behind the excavation face will move into the tunnel, thus inducing active failure of the excavation face. When the support pressure applied by the TBM to the excavation face is much greater than the required water and soil pressure to balance behind the excavation face, the soil behind the excavation face will move towards the ground surface, thus inducing passive failure of the tunnel excavation face. Whether the tunnel excavation face experiences active or passive failure, it will affect the efficiency and safety of TBM construction. How to efficiently determine the support pressure of the excavation face of a circular shield tunnel in water-rich strata and avoid active and passive failure of the tunnel excavation face is a major technical challenge.

[0004] Chinese patent CN115935482A discloses a method and system for calculating the active support force of a tunnel passing under an existing structure. This method relates to the field of rail transit engineering technology. The method includes analyzing the stress on the existing station, obtaining the geological parameters of the interlayer soil and the thickness and unit weight data of the soil above the existing station, and calculating the load on the interlayer soil and the existing station. It also involves using foundation stress to solve for the upper load on the interlayer soil to determine the upper load value at the centerline position; determining the settlement value of the existing station; determining the calculation expression for the active support force based on energy conservation; and using a planning solution to obtain the angle between the sliding rupture surface and the horizontal direction, thereby calculating the active support force at the top of the new tunnel.

[0005] In the above-mentioned method for calculating the active support force of tunnels passing under existing structures, the main approach is to derive the support force by linking the settlement value and the support force based on the law of conservation of energy. However, it does not consider the influence of groundwater seepage on pore water pressure and effective soil stress, which may underestimate the actual required support force in water-rich strata.

[0006] Therefore, a method for determining the support zone of a circular shield tunnel excavation face is needed to solve the above problems in water-rich strata. Summary of the Invention

[0007] The purpose of this invention is to provide a method for determining the support section of the excavation face of a circular shield tunnel in water-rich strata, so as to solve the problem of groundwater seepage affecting tunnel support in the prior art.

[0008] The objective of this invention is achieved as follows: This invention provides a method for determining the support zone of a circular shield tunnel excavation face in water-rich strata, comprising the following steps: S1. The finite difference method numerical simulation technology is used to simulate the groundwater seepage process during the construction of shield tunnels, and a numerical analysis model of groundwater seepage in shield tunnels in water-rich strata is constructed. S2. Run the numerical analysis model of groundwater seepage in shield tunnels in water-rich strata until the groundwater seepage stabilizes. S3. Extract the node coordinates and corresponding pore water pressure values ​​within the study area under the steady state of groundwater seepage. S4. Construct a three-dimensional mesh for the study area, and use linear interpolation technology to assign the extracted pore water pressure values ​​to the constructed three-dimensional mesh to generate a pore water pressure field that can be obtained at any point. S5. Combine the obtained pore water pressure field with the active and passive failure models of the circular shield tunnel excavation face to establish a calculation model for the safe support pressure range of the circular shield tunnel excavation face in water-rich strata, and calculate the safe support range of the excavation face.

[0009] To further explain, in step S1, the numerical analysis model for groundwater seepage in a shield tunnel in water-rich strata includes the following steps: S1-1. Obtain research parameters, including geometric parameters of the circular shield tunnel, groundwater level, permeability coefficient, and porosity; S1-2. Under the condition that the influence of the seepage boundary is negligible, determine the geometric dimensions of the numerical model based on the research parameters and construct the geometric model. S1-3, constrain the lateral and vertical seepage on the bottom surface of the geometric model, constrain the lateral seepage on the sides of the geometric model, and set the top surface of the geometric model as a free surface; S1-4. Assign the research parameters to the geometric model to establish a numerical analysis model of groundwater seepage in shield tunnels in water-rich strata. S1-5. Simulate shield tunnel excavation, excavating to the set excavation face in one go. At the same time, shell elements are used to simulate tunnel lining, and the tunnel lining is set to be impermeable, while the tunnel excavation face is set to be permeable. S1-6. Set the number of running steps and run the numerical analysis model of groundwater seepage in shield tunnels in water-rich strata until the seepage stabilizes.

[0010] To further explain, in steps S1-2, the near-surface stratum grid of the excavation face is densified to improve the accuracy of groundwater seepage simulation around the excavation face; In steps S1-5, the tunnel excavation face is set as a permeable surface to simulate the seepage behavior of groundwater in water-rich strata towards the tunnel excavation face.

[0011] To further explain, in step S3, the study area is divided based on the active and passive damage areas of the circular shield tunnel excavation face; The node coordinates and corresponding pore water pressure values ​​within the study area were extracted using the FISH language. In step S4, a three-dimensional mesh of the study area is constructed using the meshgrid and griddata languages ​​in MATLAB.

[0012] To further explain, in step S3, extracting the node coordinates and corresponding pore water pressure values ​​includes the following steps: S3-1. Delineate the study area based on the active and passive damage zones of the shield tunnel excavation face. Where D is the tunnel diameter and C is the tunnel depth; S3-2. Extract the node coordinates and corresponding pore water pressure values ​​of the numerical model constructed by the finite difference method numerical simulation technology in the specified study area using the FISH language.

[0013] To further explain, in step S4, obtaining the pore water pressure field at any point includes the following steps: S4-1. Use the meshgrid function in MATLAB to generate three-dimensional coordinate points (x, y, z) and construct a three-dimensional mesh for the study area. S4-2. After generating interpolation using MATLAB's griddata, the pore water pressure set u of the three-dimensional coordinate point set (x, y, z) is obtained. The calculation formula is as follows: In the formula, (X,Y,Z) is the set of coordinate points of the study area extracted using FISH language; P is the set of pore water pressure corresponding to the coordinate point set (X,Y,Z), and (x,y,z) are the coordinate points of the three-dimensional grid. S4-3, Through Extract any point pore water pressure value at .

[0014] The active and passive failure models are three-dimensional rotational failure models constructed based on the limit analysis kinematics method. They use spatial discretization to generate failure surfaces point by point, are applicable to complete circular excavation faces, and conform to the characteristics of rigid block rotational instability.

[0015] 8. Combining the pore water pressure field generated by MATLAB and the active and passive failure models of the shield tunnel excavation face, the upper limit theory of limit analysis is used to calculate the safe support zone of the circular shield tunnel excavation face in water-rich strata. The specific steps are as follows: S5-1. Generate active and passive damage models for the excavation face of a circular shield tunnel; S5-2. Within the theoretical framework of the upper limit analysis, and combining the obtained pore water pressure field and the active and passive theoretical models of the shield tunnel excavation face, the calculation formulas for the active and passive ultimate support pressures of the circular shield tunnel excavation face considering water-rich strata are constructed as follows: Active ultimate support pressure Calculation formula: In the formula, W γ , W d and W s These are gravity power, internal energy dissipation power, and pore water pressure power, respectively. The assumed rotational angular velocity; R The radius of rotation of the discrete surfaces of the excavation face; The rotation angle of the discrete surface; passive ultimate support pressure. Calculation formula: Gravitational power W γ Internal energy dissipation power W d and pore water pressure power W s It can be obtained by calculation using the following formula: In the formula, The soil density is [not specified]. c This represents the cohesive strength value. This is the friction angle value; To calculate the point pore water pressure value; S5-3, Based on It can calculate the safe support range of the excavation face of a circular shield tunnel in water-rich strata. .

[0016] Positive and beneficial effects: This application combines finite difference numerical simulation technology and limit analysis upper limit theory to construct a calculation model for the safe range of the excavation face of a circular shield tunnel in water-rich strata. Compared with the use of simple finite difference numerical simulation technology, it can obtain the safe range of the excavation face of a circular shield tunnel in water-rich strata more efficiently; compared with the use of simple theoretical analysis, it can obtain the safe range of the excavation face of a circular shield tunnel in water-rich strata more accurately. This application uses MATLAB to preprocess the pore water pressure values ​​extracted by FISH language, which can quickly and accurately calculate the pore water pressure values ​​at any point. The results are accurate and reliable, overcoming the shortcomings of directly using numerical simulation values ​​extracted by FISH and combining them with theoretical models, which results in multiple linear interpolations and thus time-consuming calculations. This lays the foundation for the efficient acquisition of the safe zone of the excavation face of circular shield tunnels in water-rich strata. Controlling the actual support pressure according to the calculated safe support interval can achieve the stability of the excavation face, effectively control the range of surface settlement, and effectively avoid engineering hazards such as excavation face collapse, heave and seepage damage. The deviation of pore water pressure extraction and the calculation error of support interval under various working conditions are all controlled within a reasonable range, taking into account both calculation efficiency and accuracy, providing a reliable guarantee for the safety of shield tunnel construction in water-rich strata, and reducing construction costs and safety risks. Attached Figure Description

[0017] To more clearly illustrate the technical solution of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the implementation of an embodiment of the present invention; Figure 2 The numerical model established for the embodiments of the present invention; Figure 3 These are the numerical simulation results of groundwater seepage obtained in the embodiments of the present invention; Figure 4 The three-dimensional mesh created using MATLAB is an example of an embodiment of the present invention. Figure 5 The embodiments of the present invention are based on the pore water pressure field results after MATLAB preprocessing; Figure 6 The safe zone of the excavation face is calculated for an example of this invention. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] See Figures 1-6 As shown, the present invention provides a method for determining the support section of the excavation face of a circular shield tunnel in water-rich strata, comprising the following steps: Step 1: Obtain the geological parameters of the shield tunnel section, including but not limited to the tunnel diameter, burial depth, groundwater level, unit weight of soil and rock, permeability coefficient, and porosity. In this example, the tunnel diameter D = 10m, the burial depth C = 10m, and the ratio of burial depth to tunnel diameter is 1, which belongs to the shallow burial condition; groundwater level... The tunnel is located in a water-rich stratum with high density rock and soil. Soil-rock cohesion Friction angle Permeability coefficient k=1×10 -6 m / s, porosity n=0.465.

[0021] Under the condition that the influence of the seepage boundary is negligible, the geometric dimensions of the numerical model are determined based on geological parameters, and the geometric model is constructed. The model size is selected according to step 3-1 and is larger than the delineated study area. Where D is the tunnel diameter and C is the tunnel depth; that is, the length is 100m, the width is 115m, and the height is 60m. The width in the above data is perpendicular to the tunnel axis. See [reference needed]. Figure 2 As shown, the grid within a 4m radius of the excavation face is refined, with a grid size of 0.3m × 0.3m × 0.3m. The grid size in the remaining areas is 0.7m × 0.7m × 0.7m, in order to improve the accuracy of groundwater seepage simulation. In the geometric model, the lateral and vertical seepage on the bottom surface of the geometric model is constrained, the lateral seepage on the sides of the geometric model is constrained, and the top surface of the geometric model is set as a free surface. Permeability parameter k, porosity n, and unit weight of soil and rock The values ​​are assigned to the geometric model to establish a numerical analysis model of groundwater seepage in shield tunnels in water-rich strata; the soil is modeled as saturated soil, and the soil-rock cohesion c and internal friction angle are also substituted. Additional soil strength parameters have been added to help the model accurately reflect the actual subsurface characteristics; see the attached diagram in the instruction manual. Figure 2 As shown, Figure 2 The numerical analysis model shown has completed shield excavation and lining support, demonstrating the position of the shield tunnel in the geometric model; Run the numerical analysis model of groundwater seepage in shield tunnels in water-rich strata until the groundwater seepage stabilizes; see the attached diagram in the instruction manual for details. Figure 3 As shown, the process runs for 400,000 steps with a time step size of 3.85 × 10⁻⁶. -2 s, run until the groundwater seepage velocity and pore water pressure within the model stabilize, see details. Figure 3 , Figure 3 The results of groundwater seepage calculated based on a numerical analysis model are shown. The pore water pressure gradually increases from the top to the bottom of the figure, with the middle being a transition zone. The inner side of the tunnel borehole is similar to the upper part, indicating that the pore water pressure here is at a low level. This is because after the tunnel is excavated, the space originally occupied by soil particles and water is released, and the water in the borehole is discharged through the drainage system, reducing the water pressure and thus achieving the purpose of controlling seepage and preventing water inrush.

[0022] The second step involves using the active and passive damage areas of the circular shield tunnel excavation face as a basis, and strictly following the procedures outlined in step 3-1 regarding the "study area". The delineation requirements are based on the parameters D=10m and C=10m in this embodiment. The research area is calculated and divided to ensure complete coverage of the range that may be involved in active and passive damage. The specific calculations and delineation are as follows: the length of the study area is 2D = 2 × 10 = 20m, the width of the study area is 1.5D = 1.5 × 10 = 15m, and the height of the study area is C + D = 10 + 10 = 20m; where the width of the study area is perpendicular to the tunnel axis. In summary, the study area is defined as follows: a total length of 20m along the tunnel axis, extending from 10m in front of the excavation face to 10m behind the excavation face; a total width of 15m perpendicular to the tunnel axis, extending from 7.5m to 7.5m to the left and right sides of the excavation face; and a total vertical height of 20m, extending from the ground surface to 10m below the tunnel bottom. This design is suitable for the damage range characteristics of a 10m diameter tunnel, strictly conforms to the defined standards, and ensures that the study area is entirely within the numerical model constructed in steps S1-2, thus avoiding the influence of boundary effects. The third step involves using the FISH language to extract the node coordinates (X, Y, Z) and the corresponding pore water pressure values ​​P for the specified area. A total of 15,600 coordinate points are extracted based on the grid density. Then, the groundwater level H is used as the basis for further analysis. W =10m, soil unit weight γ=20kN / m³, theoretically calculated pore water pressure benchmark value is γ×H W =20×10=200kPa. The actual extracted pore water pressure value ranges from 185.6kPa to 212.8kPa. The pore water pressure value around the excavation face is concentrated between 200.0kPa and 212.8kPa, which is within 6% of the theoretical value. This verifies the rationality and accuracy of the seepage numerical analysis model.

[0023] The fourth step involves constructing a three-dimensional mesh for the study area using MATLAB. The meshgrid function in MATLAB is used to generate three-dimensional coordinate points (x, y, z) corresponding to the study area. The mesh spacing is consistent with the densified area of ​​the numerical model. Linear interpolation technology, namely the griddata function in MATLAB, is used to assign the extracted pore water pressure values ​​to the three-dimensional mesh constructed by MATLAB, thereby obtaining a pore water pressure field that can be efficiently extracted at any point. The interpolation error is controlled within 4.8%, which meets the accuracy requirements for the calculation of the support section.

[0024] Figure 4The study demonstrates a three-dimensional mesh for a specified research area built using MATLAB. This hexahedral mesh is the numerical calculation unit, and each small square node contains the mechanical and hydrological parameters of the soil. The mechanical parameters of the soil mainly include cohesion, internal friction angle, permeability coefficient, and other mechanical properties. When simulating tunnel excavation, the pore water pressure change of each unit is calculated one by one, so as to obtain a numerical solution that is more in line with the actual engineering and provide a reference for support design. Figure 5 This study demonstrates how pore water pressure fields at any point can be efficiently extracted using MATLAB. In the structure of soil 5, the top of the model is in a region with lower data, the bottom region has higher values, the middle region is in a transitional setting, and the values ​​are lower at the tunnel location. The pore water pressure values ​​increase rapidly in the bottom region of the tunnel, while the pore water pressure values ​​gradually decrease upwards from the top of the tunnel.

[0025] Using MATLAB's griddata tool to generate an interpolated set of 3D coordinate points ( x , y , z ) pore water pressure collection u : , In the formula, ( X , Y , Z (This refers to the set of coordinate points for the study area extracted using the FISH language;) P For the set of coordinate points ( X , Y , Z The corresponding pore water pressure set; The following command can be used to efficiently extract any point (x). i ,y i ,z i The pore water pressure value u at () i : , Referring to https: / / doi.org / 10.1002 / nag.962, active and passive failure models of the excavation face of a circular shield tunnel were generated. This model is a three-dimensional rotational failure model based on the limit analysis kinematics method, and the failure surface is generated point by point using spatial discretization technology. Combining the parameters of the 10m large-diameter tunnel in this embodiment, the soil parameters cohesion c=15kPa and internal friction angle were substituted. The tunnel parameters are: diameter D=10m, burial depth C=10m. The active and passive failure models are constructed to ensure that the models are compatible with the working conditions of this embodiment. Within the theoretical framework of the upper limit analysis, combined with the obtained pore water pressure field and the main and passive theoretical models of the circular shield tunnel excavation face, and substituting the soil and rock parameters in this embodiment, a calculation model for the main and passive ultimate support pressure of the excavation face is constructed through the power balance principle to calculate the ultimate support pressure. Active ultimate support pressure Calculation formula: , In the formula, W γ , W d and W s These are gravity power, internal energy dissipation power, and pore water pressure power, respectively. The assumed rotational angular velocity; R The radius of rotation of the discrete surfaces of the excavation face; The rotation angle of the discrete surface; Passive ultimate support pressure Calculation formula: Gravitational power W γ Internal energy dissipation power W d and pore water pressure power W s It can be obtained by calculation using the following formula: , In the formula, The soil density is [not specified]. c This represents the cohesive strength value. This is the friction angle value; u To calculate the pore water pressure value; safety support zone of the excavation face of a circular shield tunnel in water-bearing strata. It can be calculated as: Combine formulas (1) to (8) to calculate the safe support zone of the excavation face.

[0026] Figure 6 This invention illustrates the safe support pressure range at the tunnel excavation face according to an embodiment of the present invention. Figure 6 As the friction angle changes, the active and passive ultimate support pressures also change. The bottom edge of the shaded area represents the active ultimate support pressure value, which gradually decreases as the friction angle increases. For every 5° increase in the friction angle, the active ultimate pressure decreases by approximately 15%. The passive ultimate support pressure value is located at the top of the shaded area. Its value increases rapidly with the increase of the friction angle. For every 5° increase in the friction angle, the passive ultimate pressure can be increased by about 50%. The shaded area between the passive ultimate support pressure value and the active ultimate support pressure value is the safe support range, which widens as the internal friction angle increases.

[0027] When the friction angle At that time, the active ultimate support pressure was calculated. Passive ultimate support pressure When the friction angle At that time, the active ultimate support pressure was calculated. Passive ultimate support pressure In summary, the calculated safe support range for the excavation face is 85.1 kPa - 10100.7 kPa. Combined internal friction angle Based on all working conditions, the safe support range for the excavation face of the circular shield tunnel in the water-rich strata in this embodiment was finally determined to be 108.5 kPa-5030.8 kPa.

[0028] In this embodiment, the actual support pressure was controlled between 220kPa and 400kPa, taking into account the actual construction safety redundancy requirements. No collapse, uplift, or seepage damage occurred at the excavation face during construction, and the surface settlement was controlled within 5mm, which verified the effectiveness and applicability of this method. At the same time, it accurately matched all the parameter calculation requirements given in this embodiment.

[0029] The second embodiment differs from the first embodiment in that: In this embodiment, the tunnel diameter D = 10m and the burial depth C = 15m, which is a transitional condition between shallow and deep burial; the groundwater level H... W =12m, unit weight of soil and rock Soil-rock cohesion c =15kPa, friction angle Permeability coefficient The porosity n=0.465; the study area is defined as 2D×1.5D×(C+D) (20m×15m×25m). After calculation using equations (1)-(8), according to At that time, the safe support range of the excavation face was calculated to be 287.7kPa-7526.8kPa. In practice, the excavation face can be stabilized and the surface settlement ≤5.2mm when the support pressure is controlled between 300kPa-1000kPa.

[0030] The third embodiment differs from the first embodiment in that: In this embodiment, the tunnel diameter D = 9m and the burial depth C = 9m, which is a shallow burial condition; the groundwater level H... W =7m, unit weight of soil and rock Soil-rock cohesion c =16kPa, friction angle Permeability coefficient / s, porosity n=0.445; the study area was delineated according to 2D×1.5D×(C+D) (18m×13.5m×18m). After calculation using equations (1)-(8), according to j =28°-38° At that time, the safe support range of the excavation face was calculated to be 167.7kPa-5596.8kPa. In practice, the excavation face can be stabilized and the surface settlement ≤4.6mm when the support pressure is controlled between 190kPa-1000kPa.

[0031] The fourth embodiment differs from the first embodiment in that: In this embodiment, the tunnel diameter D = 13m and the burial depth C = 26m, which falls under the deep burial condition; the groundwater level H... W =22m, unit weight of soil and rock Soil-rock cohesion c =21kPa, friction angle Permeability coefficient The porosity n=0.50; the study area was defined as 2D×1.5D×(C+D) (26m×19.5m×39m). After calculation using equations (1)-(8), according to At that time, the safe support range of the excavation face was calculated to be 385.7kPa-9060.8kPa. In practice, the excavation face can be stabilized and the surface settlement ≤5.6mm when the support pressure is controlled at 450kPa-1000kPa.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining a support interval of a circular shield tunnel face in a water-rich stratum, characterized in that: Includes the following steps: S1. The finite difference method numerical simulation technology is used to simulate the groundwater seepage process during the construction of shield tunnels, and a numerical analysis model of groundwater seepage in shield tunnels in water-rich strata is constructed. S2. Run the numerical analysis model of groundwater seepage in shield tunnels in water-rich strata until the groundwater seepage stabilizes. S3. Extract the node coordinates and corresponding pore water pressure values ​​within the study area under the steady state of groundwater seepage. S4. Construct a three-dimensional mesh for the study area, and use linear interpolation technology to assign the extracted pore water pressure values ​​to the constructed three-dimensional mesh to generate a pore water pressure field that can be obtained at any point. S5. Combine the obtained pore water pressure field with the active and passive failure models of the circular shield tunnel excavation face to establish a calculation model for the safe support pressure range of the circular shield tunnel excavation face in water-rich strata, and calculate the safe support range of the excavation face.

2. The method of claim 1, wherein: In step S1, the numerical analysis model for groundwater seepage in shield tunnels in water-rich strata includes the following steps: S1-1. Obtain research parameters, including geometric parameters of the circular shield tunnel, groundwater level, permeability coefficient, and porosity; S1-2. Under the premise that the influence of the seepage boundary is negligible, determine the geometric dimensions of the numerical model based on the research parameters and construct the geometric model. S1-3, constrain the lateral and vertical seepage on the bottom surface of the geometric model, constrain the lateral seepage on the sides of the geometric model, and set the top surface of the geometric model as a free surface; S1-4. Assign the research parameters to the geometric model to establish a numerical analysis model of groundwater seepage in shield tunnels in water-rich strata. S1-5. Simulate shield tunnel excavation, excavating to the set excavation face in one go. At the same time, shell elements are used to simulate tunnel lining, and the tunnel lining is set to be impermeable, while the tunnel excavation face is set to be permeable. S1-6. Set the number of running steps and run the numerical analysis model of groundwater seepage in shield tunnels in water-rich strata until the seepage stabilizes.

3. The method of claim 1, wherein: In steps S1-2, the near-surface mesh of the excavation face is densified to improve the accuracy of groundwater seepage simulation around the excavation face; In steps S1-5, the tunnel excavation face is set as a permeable surface to simulate the seepage behavior of groundwater in water-rich strata towards the tunnel excavation face.

4. The method of claim 3, wherein: In step S3, the study area is divided based on the active and passive damage areas of the circular shield tunnel excavation face; The node coordinates and corresponding pore water pressure values ​​within the study area were extracted using the FISH language. In step S4, a three-dimensional mesh of the study area is constructed using the meshgrid and griddata languages ​​in MATLAB.

5. The method for determining the support interval of the circular shield tunnel face in the water-rich formation according to claim 4, characterized in that: In step S3, the node coordinates and corresponding pore water pressure values ​​are extracted, including the following steps: S3-1, according to the main and passive damage areas of the shield tunnel excavation face, the research area is delimited wherein D is the diameter of the tunnel and C is the buried depth of the tunnel. S3-2. Extract the node coordinates and corresponding pore water pressure values ​​of the numerical model constructed by the finite difference method numerical simulation technology in the specified study area using the FISH language.

6. The method for determining the support interval of the circular shield tunnel face in the water-rich formation according to claim 5, characterized in that: In step S4, the pore water pressure field at any point is obtained, including the following steps: S4-1, using the meshgrid function in MATLAB to generate three-dimensional coordinate points (x,y,z) and construct a three-dimensional mesh for the study area; S4-2. After generating interpolation using MATLAB's griddata, the pore water pressure set u of the three-dimensional coordinate point set (x, y, z) is obtained. The calculation formula is as follows: u=griddata(X,Y,Z,P,x,y,z) In the formula, (X, Y, Z) is a set of coordinate points of a numerical simulation of a research area extracted based on FISH language; P is a set of pore water pressures corresponding to the set of coordinate points (X, Y, Z); (x, y, z) is a three-dimensional grid coordinate point; S4-3, by u i =u(x i ,y i ,z i ), extracts a pore water pressure value u i at an arbitrary point (x i ,y i ,z i ).

7. The method for determining the support interval of the circular shield tunnel face in the water-rich formation according to claim 6, characterized in that: The active and passive failure models are three-dimensional rotational failure models constructed based on the limit analysis kinematics method. They use spatial discretization to generate failure surfaces point by point, are applicable to complete circular excavation faces, and conform to the characteristics of rigid block rotational instability.

8. The method for determining the support interval of the circular shield tunnel face in the water-rich formation according to claim 7, characterized in that: Combining the pore water pressure field generated by MATLAB and the active and passive failure models of the shield tunnel excavation face, the safe support interval of the circular shield tunnel excavation face in water-rich strata is calculated using the upper limit theory of limit analysis. The specific steps are as follows: S5-1. Generate active and passive damage models for the excavation face of a circular shield tunnel; S5-2. Within the theoretical framework of the upper limit analysis, and combining the obtained pore water pressure field and the active and passive theoretical models of the shield tunnel excavation face, the calculation formulas for the active and passive ultimate support pressures of the circular shield tunnel excavation face considering water-rich strata are constructed as follows: Active ultimate support pressure s t Calculation formula: In the formula, W γ , W d and W s These are gravity power, internal energy dissipation power, and pore water pressure power, respectively. The assumed rotational angular velocity; R The radius of rotation of the discrete surfaces of the excavation face; The rotation angle of the discrete surface; passive ultimate support pressure. Calculation formula: Gravitational power W γ Internal energy dissipation power W d and pore water pressure power W s It can be obtained by calculation using the following formula: In the formula, The soil density is [not specified]. This represents the cohesive strength value. This is the friction angle value; To calculate the point pore water pressure value; S5-3, based on formula It can calculate the safe support range of the excavation face of a circular shield tunnel in water-rich strata. .

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