Method for analyzing influence of underground excavation under-crossing on existing subway station

Abstract

The invention relates to an underground engineering construction design technology, discloses a method for analyzing the influence of underground excavation under-crossing on an existing subway station, and improves the efficiency and precision of analyzing the influence of underground excavation under-crossing construction on the existing subway station. The method comprises the steps that by defining a structure and geometrical shapes and material attributes of a stratum, boundary conditions and external loads are set, grid division is carried out, and a finite element three-dimensional basic calculation model is constructed; according to theories of porous media and the like, a multi-physical field coupling model of a seepage-deformation-temperature full coupling effect is constructed; the rigidity of the underground excavation vertical pile foundation is calculated, and the rigidity of the underground excavation vertical pile foundation is corrected based on the influence factors of the soil squeezing effect and the negative friction resistance; subsurface excavation construction is subdivided into a plurality of stages, structural stress, deformation and stratum displacement are calculated through an incremental method, and the timeliness of a supporting structure and the influence of different excavation modes on stratum disturbance are analyzed; and obtaining a structural response through finite element iteration solution, and judging the influence of underground excavation under-crossing on the existing subway station.

Description

Technical Field

[0001] The present invention relates to the technical field of underground engineering construction design, and particularly to a method for analyzing the influence of undercutting in the dark on existing subway stations. Background Art

[0002] In the construction of underground projects, the construction method of undercutting in the dark has become one of the important methods for the construction of infrastructure such as subways and tunnels. Due to its characteristics of small environmental impact, high construction flexibility, and adaptability to complex geological conditions, the undercutting construction technology is widely used in the construction of urban rail transit and other underground projects. During the undercutting construction process, the rationality of the construction method and technology is directly related to the safety and stability of the existing structure.

[0003] Undercutting construction usually involves excavation operations under or near existing subway stations. The ground deformation, stress redistribution, and disturbance to the existing structure during the construction process may affect the structural safety and normal use of the existing subway stations. Therefore, accurately evaluating the influence of undercutting construction on existing subway stations is of great significance for optimizing the construction plan and ensuring operation safety.

[0004] Currently, in the engineering practice of analyzing the influence of undercutting in the dark on existing subway stations, numerical simulation methods based on finite element analysis are usually adopted. This method constructs a three-dimensional numerical model manually to simulate the complex mechanical behaviors of ground deformation, the stress of the existing station structure, and the construction interaction during the undercutting construction process. The specific implementation is as follows:

[0005] 1. Manual definition and modeling

[0006] In this process, researchers manually define various parameters of the numerical model according to the actual requirements of the undercutting project in the dark, including the geometric dimensions, material properties, and interaction relationship between the ground and the structure of the existing station structure. These parameters are usually set in combination with engineering experience, geological exploration data, and design standards. The modeling process is completed through professional numerical simulation software and requires multiple adjustments and verifications to ensure the rationality of the model. The specific steps include:

[0007] (1) Input structure parameters: Define the geometric dimensions, material properties, and cross-sectional attributes of the existing station and the undercut tunnel. For example, determine the length, width, and height of the main structure of the station according to the design drawings, as well as the material type (such as the strength grade of concrete, etc.) and cross-sectional dimensions of each component.

[0008] (2) Set the interaction relationship: According to the physical and mechanical properties of the ground, set the interaction relationship between the ground and the structure, such as using spring elements to simulate the constraint of the ground on the structure. The parameters such as the stiffness of the spring elements are determined according to the physical and mechanical parameters of the ground, such as the elastic modulus and Poisson's ratio of the ground.

[0009] (3)Determine the boundary conditions: Set the boundary conditions and external loads of the model, such as formation stress, groundwater pressure, and construction disturbance effects. The formation stress is determined based on the in-situ stress test results of geological exploration, and the groundwater pressure is calculated according to the depth of the groundwater level and the unit weight of water.

[0010] (4)Calibrate the model: Through multiple simulations and adjustments, optimize the model parameters to make the simulation results consistent with engineering experience or existing data. For example, compare the formation settlement results calculated by the model with the actual monitoring data of similar projects, and continuously adjust the model parameters until the deviation between the two is within an acceptable range.

[0011] 2. Segmented discrete model and local refinement

[0012] In this process, to improve the model accuracy, the mined tunnel and the existing station structure are usually discretized into multiple elements (such as beam elements, shell elements, or solid elements) to form a finite element model. For complex working conditions, such as non-uniform formations or asymmetric load cases, local areas may be further refined for modeling to capture stress concentration and deformation behavior, which can improve the flexibility and accuracy of the model to a certain extent and is suitable for analyzing local stress characteristics and sensitive areas.

[0013] 3. Static and dynamic simulation analysis

[0014] In this process, based on the constructed numerical model, researchers analyze the structural behavior of the existing station during the mined-under construction through finite element analysis tools. This includes static analysis (such as structural stability and formation deformation) and dynamic analysis (such as construction disturbance effects and formation consolidation effects), which are commonly used to evaluate formation settlement, stress distribution of the existing station structure, structural stability, etc., and assist in engineering design and construction decisions.

[0015] Although the existing finite element-based numerical simulation schemes can simulate the impact of mined-under construction on existing subway stations to a certain extent, they have the following limitations:

[0016] (1)Unable to dynamically consider the construction process

[0017] In the process of finite element analysis, the total stress method model is mostly used, that is, it is assumed that the impact of the construction process on the structure and formation is static and one-time, and it cannot dynamically reflect the progressive excavation, support, and structural stress changes during the construction process. This model ignores the spatio-temporal effects during the construction process and is difficult to simulate the formation stress release, deformation accumulation, and dynamic response of the existing structure during the construction process. For example, in actual construction, as the excavation progresses, the formation stress is gradually released and the structural stress is constantly changing, but the total stress method model cannot accurately reflect this process.

[0018] Due to the inability to consider the dynamics of the construction process, existing methods are difficult to accurately predict the impact of construction on existing subway stations. Especially under complex geological conditions, the dynamic changes during construction may cause the deformation and stress of the existing structure to exceed the design expectations, increasing the construction risk.

[0019] (2) Single boundary conditions, without considering the effect of groundwater

[0020] Existing technologies have relatively simple boundary conditions. Usually, only formation stress and external loads are considered, and the effect of groundwater is not fully taken into account. The presence of groundwater will significantly affect the mechanical properties of the formation and the stability of the existing structure. Especially during the excavation construction, groundwater flow may cause problems such as formation settlement, deformation of the existing structure, and even leakage. For example, during the excavation construction in water-rich formations, the seepage of groundwater will change the distribution of effective stress in the formation, thereby affecting the stability of the structure. However, existing models often ignore this factor.

[0021] Due to the lack of consideration of the effect of groundwater, when existing models analyze the impact of under-excavation construction on existing subway stations, they may underestimate the formation deformation and the stress of the existing structure, resulting in the lack of pertinence and safety of the design and construction plans.

[0022] (3) The model is complex and not simplified

[0023] In the process of modeling by existing technologies, complex three-dimensional finite element models are often directly adopted without reasonable simplification of the models. Although high-precision models can reflect more details, they also lead to a significant increase in computational complexity, long computational time, and difficulty in efficient adjustment and optimization.

[0024] Since the complex and unsimplified model not only limits the computational efficiency but also increases the modeling difficulty and cost, it is difficult to meet the requirements of rapid response and real-time monitoring in engineering practice. In addition, it is easy to introduce human errors during the parameter setting and calibration processes of complex models, reducing the accuracy and reliability of the models.

[0025] In summary, the existing methods for analyzing the impact of under-excavation construction on existing subway stations have the following defects: The model construction relies on a large number of manual operations and empirical judgments, and cannot dynamically reflect the spatio-temporal effects of the construction process; The boundary conditions are set simply, and the influence of groundwater on the formation and structure is not fully considered; The model is complex and not simplified, resulting in high computational complexity and low efficiency. These defects make it difficult for existing methods to meet the actual needs of rapid engineering decision-making and optimized design, highlighting their limitations in practical applications. Therefore, there is an urgent need to improve the modeling and simulation technologies to improve efficiency and accuracy. Summary of the Invention

[0026] The technical problem to be solved by the present invention is to propose a method for analyzing the influence of underground excavation under a existing subway station, improve the efficiency and accuracy of the influence analysis of underground excavation construction on the existing subway station, and at the same time consider the influence of the settlement deformation of the pile foundation itself, so as to provide more efficient and reliable technical support for the design and construction of complex underground projects.

[0027] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0028] A method for analyzing the influence of underground excavation under a existing subway station, comprising the following steps:

[0029] S1. By defining the geometric shapes and material properties of the structure and the stratum, setting boundary conditions and external loads, and performing mesh division, a finite element three-dimensional foundation calculation model is constructed;

[0030] S2. On the basis of the finite element three-dimensional foundation calculation model, a multi-physical field coupling model considering the full coupling effect of seepage-deformation-temperature is constructed;

[0031] S3. Calculate the stiffness of the underground excavation vertical pile foundation, and correct the stiffness of the underground excavation vertical pile foundation based on the influencing factors of soil compaction effect and negative skin friction, and apply the corrected stiffness of the underground excavation vertical pile foundation to the finite element three-dimensional foundation calculation model;

[0032] S4. Subdivide the underground excavation construction into multiple stages, simulate the processes of stratum unloading, support structure construction, and precipitation soil-water-solid coupling, calculate the structural stress, deformation and stratum displacement by using the incremental method, and analyze the timeliness of the support structure and the influence of different excavation methods on stratum disturbance;

[0033] S5. Through finite element iterative solution, obtain the structural response and evaluate the influence of underground excavation under the existing subway station.

[0034] Further, in step S1, when constructing the finite element three-dimensional foundation calculation model, adaptive mesh division is adopted, and the mesh density is adjusted according to the stress gradient. Among them, the stress gradient tensor calculation formula is:

[0035] ;

[0036] Among them, is the stress tensor component, is the coordinate component, is the unit vector;

[0037] Calculate the global stress gradient of the model through this formula, densify the mesh in the area adjacent to the underground excavation tunnel and the existing subway station, and increase the mesh size in the area where the stress changes gently.

[0038] Furthermore, in step S1, the constructed three-dimensional finite element basic calculation model includes stratified formations, and different formations adopt different constitutive models; the three-dimensional finite element basic calculation model is defined with boundary conditions, including fixed boundaries and free boundaries, and external loads, ground stresses, friction between the subway station and the formation, and additional loads caused by construction disturbances are considered; the fixed boundaries restrict the displacement degrees of freedom in the boundary directions of the model to simulate the bedrock constraints; the free boundaries allow the structure to deform according to the actual situation.

[0039] Furthermore, in step S2, a multi-physical field coupling model considering the full coupling effect of seepage-deformation-temperature is constructed, including:

[0040] Based on the porous medium theory, a seepage model is established. The seepage equation and the solid deformation control equation are coupled according to the mixture theory, and the temperature field and the fluid-solid coupling system are coupled through the energy conservation equation, thereby constructing a multi-physical field coupling model considering the full coupling effect of seepage-deformation-temperature;

[0041] The control equation of the seepage model is the steady-state seepage equation coupled by the anisotropic Darcy's law and the continuity equation:

[0042] ;

[0043] where is the permeability coefficient tensor, is the water head value.

[0044] Furthermore, the seepage equation and the solid deformation control equation are coupled through the mixture theory, and the control equation of the coupled fluid-solid coupling system is:

[0045] , ;

[0046] where is the effective stress tensor, are the displacement components, is the body force component, is the density of water, is the porosity, is the seepage velocity;

[0047] The temperature field and the fluid-solid coupling system are coupled through the energy conservation equation, thereby constructing a multi-physical field coupling model considering the full coupling effect of seepage-deformation-temperature, and its control equation is:

[0048] ;

[0049] where is the equivalent heat capacity of the rock and the fluid; is the equivalent thermal conductivity; is the fluid convective heat transfer term; is the heat source term converted from the mechanical work of solid deformation; T represents temperature.

[0050] Furthermore, when constructing a multi-physics coupling model considering the full coupling effect of seepage-deformation-temperature, it also includes:

[0051] Modify the permeability tensor according to the attitude parameters of faults and joints in the formation:

[0052] ;

[0053] where, is the matrix permeability tensor; is the permeability increment of the th fault; is the attenuation coefficient of tectonic influence, is the attitude angle of the th fault, and n is the number of faults in the formation; the modified tensor is used in the fluid-solid coupling equation to characterize the guiding effect of geological structures on seepage paths;

[0054] Introduce the correction relationship of permeability by the temperature field:

[0055] ;

[0056] where, is the permeability at temperature , is the initial permeability, is the fluid viscosity at temperature , is the fluid viscosity at the reference temperature, is the coefficient of thermal expansion of the rock, calibrated by thermodynamic experiments.

[0057] Furthermore, in step S3, the method for calculating the stiffness of the mined vertical pile foundation is:

[0058] Calculate the pile foundation force and displacement through the theoretical load and the elastic foundation model:

[0059] ;

[0060] where, is the unit weight of overburden; is the thickness of overburden; is the cross-sectional area of the pile; is the self-weight of the structure; is the live load; is the coefficient of subgrade reaction; is the pile length; is the flexural stiffness of the pile;

[0061] Based on the pile foundation force and displacement , calculate the initial stiffness of the vertical pile foundation in the mined - out area.

[0062] Furthermore, in step S3, the stiffness of the vertical pile foundation in the mined - out area is corrected based on the soil compaction effect, negative skin friction and other influencing factors, including:

[0063] ;

[0064] Among them, is the initial stiffness of the vertical pile foundation in the mined - out area, is the pile material hardening model, is the pile - soil contact stiffness.

[0065] Furthermore, in step S4, the incremental method is used to calculate the structural stress, strain and formation displacement, including:

[0066] ;

[0067] Among them, is the stress increment in the th stage, is the elastic stiffness matrix, is the strain increment in the th stage.

[0068] Furthermore, in step S4, during the simulation of the formation unloading, the construction of the support structure and the coupling of seepage and solid in the precipitation process, the time step is dynamically adjusted, and it satisfies:

[0069] ;

[0070] Among them, is a constant, is the characteristic length, is the elastic modulus, is the density.

[0071] The beneficial effects of the present invention are:

[0072] (1) Considering the spatio - temporal effect, dynamically simulating the construction process:

[0073] The present invention considers the gradual loading during the construction process, the release of formation stress, the accumulation of deformation and the dynamic response of the existing structure. By dividing the construction process into multiple stages, simulating the excavation, support and other operations in each stage, and real - time tracking the mechanical changes of the structure and the formation, it can more accurately predict the impact of the construction on the existing subway station and provide a more reliable guarantee for construction safety.

[0074] (2)Comprehensively consider the effect of groundwater and optimize the boundary conditions:

[0075] By introducing a fluid-solid coupling mechanical model, this invention takes into account factors such as the seepage path of groundwater and the change of pore water pressure in the model, and then comprehensively considers the influence of groundwater flow on the mechanical properties of the formation and the stability of existing structures, so as to more accurately simulate the formation settlement, structural deformation and leakage risk, and improve the accuracy and safety of the analysis.

[0076] (3)Consider the influence of the settlement and deformation of the pile foundation itself to improve the calculation accuracy:

[0077] By introducing a calculation model for the settlement and deformation of the pile foundation, this invention takes into account the influence of the settlement and deformation of the pile foundation on the existing structure. In addition, it also considers the influence of factors such as soil compaction effect and negative skin friction during the construction of the pile foundation on the settlement. By comprehensively considering the influence of various factors on the settlement of the pile foundation, more accurate data can be provided for the safety assessment of the subway station structure.

[0078] (4)Simplify the model construction to improve the calculation efficiency:

[0079] When constructing the finite element three-dimensional basic calculation model, this invention adopts the adaptive mesh generation technology, densifies the mesh in the key areas, and appropriately enlarges the mesh size in the non-key areas, so as to improve the calculation efficiency while ensuring the calculation accuracy.

[0080] In summary, this invention improves the efficiency and accuracy of the analysis of the influence of the mined-under construction on the existing subway station, and at the same time considers the influence of the settlement and deformation of the pile foundation itself, providing more efficient and reliable technical support for the design and construction of complex underground projects. Brief Description of the Drawings

[0081] Figure 1 It is a flow chart of the method for analyzing the influence of the mined-under construction on the existing subway station in this invention. Detailed Embodiment

[0082] The present invention aims to provide a method for analyzing the influence of mined tunneling under an existing subway station, improving the efficiency and accuracy of analyzing the influence of mined tunneling construction on the existing subway station. Meanwhile, considering the influence of the settlement and deformation of the pile foundation itself, it provides more efficient and reliable technical support for the design and construction of complex underground projects. Its core idea is: (1) The existing technology adopts the total stress method model, which cannot dynamically reflect the gradual excavation, support, and structural stress changes during the construction process, ignoring the spatio-temporal effect of the construction process. To address this problem, the present invention considers the gradual loading, stratum stress release, deformation accumulation, and dynamic response of the existing structure during the construction process. By dividing the construction process into multiple stages, simulating operations such as excavation and support in each stage, and real-time tracking the mechanical changes of the structure and the stratum, it can more accurately predict the influence of the construction on the existing subway station and provide more reliable guarantee for construction safety. (2) The boundary conditions set in the existing technology are relatively single, and the influence of groundwater on the stability of the stratum and the existing structure is not fully considered. To address this problem, the present invention introduces a fluid-solid coupling mechanical model, considering factors such as the seepage path of groundwater and the change of pore water pressure in the model, and then comprehensively considering the influence of groundwater flow on the mechanical properties of the stratum and the stability of the existing structure, so as to more accurately simulate the stratum settlement, structural deformation, and leakage risk, improving the accuracy and safety of the analysis. (3) In the existing technology, the influence of the settlement and deformation of the pile foundation on the existing subway station is not fully considered, resulting in a large deviation in the calculation results. To address this problem, the present invention introduces a calculation model for the settlement and deformation of the pile foundation, considering the influence of pile foundation settlement and deformation on the existing structure. In addition, it also considers the influence of factors such as soil compaction effect and negative skin friction during the pile foundation construction process on the settlement. By comprehensively considering the influence of various factors on the pile foundation settlement, it provides more accurate data for the structural safety assessment of the subway station. (4) The existing technology adopts a complex three-dimensional finite element model without reasonable simplification of the model, resulting in high calculation complexity and low efficiency. To address this problem, when constructing the finite element three-dimensional basic calculation model, the present invention adopts an adaptive mesh generation technology, densifying the mesh in the key areas and appropriately enlarging the mesh size in the non-key areas, improving the calculation efficiency while ensuring the calculation accuracy.

[0083] In terms of specific implementation, the method flow of the present invention for analyzing the influence of mined tunneling under an existing subway station is shown in Figure 1 , which includes the following implementation processes:

[0084] S1. By defining the geometric shapes and material properties of the structure and the stratum, setting boundary conditions and external loads, and performing mesh generation, a finite element three-dimensional basic calculation model is constructed;

[0085] In this step, the finite element basic calculation model includes a stratum modeled in layers, and different strata adopt different constitutive models. For example: the sandy soil layer adopts the Mohr - Coulomb model, and the mechanical constitutive model formula of the sandy soil layer is:

[0086] ;

[0087] Among them, and are the principal stresses, is the cohesion, is the internal friction angle. Obtain the sand layer parameters according to the geological exploration report and substitute them into the formula to accurately simulate the mechanical response of the sand layer.

[0088] The finite element basic calculation model needs to define appropriate boundary conditions, including fixed boundaries and free boundaries, and consider external loads, in-situ stresses, friction between the subway station and the formation, and additional loads caused by construction disturbances. The fixed boundary restricts the displacement degrees of freedom in a specific direction of the model boundary to simulate the bedrock constraint; the free boundary allows the structure to deform according to the actual situation.

[0089] In the way of dividing the finite element mesh, adaptive mesh division is adopted, and the mesh density is adjusted according to the stress gradient. The stress gradient tensor calculation formula is:

[0090] ;

[0091] Among them, is the stress tensor component, is the coordinate component, is the unit vector. Calculate the stress gradient of the entire model domain through this formula, densify the mesh in key areas such as the vicinity of the mined tunnel and the existing subway station, and appropriately increase the mesh size in areas where the stress changes gently to improve the calculation accuracy while controlling the calculation amount.

[0092] S2. On the basis of the finite element three-dimensional basic calculation model, construct a multi-physical field coupling model considering the full coupling effect of seepage-deformation-temperature;

[0093] In this step, first establish a seepage model based on the porous medium theory and describe soil deformation by applying Biot's consolidation theory. And consider the influence of faults and joints on the permeability tensor to establish a modified model. By introducing the influence of the temperature field on the permeability, realize the coupled analysis of the seepage field, stress field and temperature field to obtain an accurate fluid-solid coupling response.

[0094] The control equation of the seepage model is the steady seepage equation coupled by the anisotropic Darcy's law and the continuity equation:

[0095] ;

[0096] Among them, is the permeability coefficient tensor, is the water head value;

[0097] The finite volume method is used to discretize the seepage equation, and the discretized form of the control unit is:

[0098] ;

[0099] where, is the area of the face , is the distance from the face to the unit center , is the equivalent permeability tensor of the face .

[0100] The seepage equation and the solid deformation control equation are coupled through the mixture theory, and the control equation of the fluid-solid coupling system is:

[0101] , ;

[0102] where, is the effective stress tensor, is the displacement component, is the medium density, is the volume force component, is the density of water, is the porosity, is the seepage velocity. Specifically, according to the physical and mechanical properties of the actual rock and soil mass, the parameters required for the control equation are customized in the multi-physical field coupling setting module to simulate the fluid-solid coupling process.

[0103] According to the occurrence parameters (dip direction, dip angle, density) of faults and joints in the formation, the permeability tensor is corrected:

[0104] ;

[0105] where, is the matrix permeability tensor; is the permeability increment of the th fault / joint; is the tectonic influence attenuation coefficient, is the occurrence angle of the th fault; the corrected tensor is used in the fluid-solid coupling equation to characterize the guiding effect of geological structures on the seepage path.

[0106] The correction relationship of the permeability by the temperature field is introduced:

[0107] ;

[0108] where, is the permeability at temperature , is the initial permeability, is the temperature of the fluid at is the fluid viscosity at the reference temperature, is the coefficient of thermal expansion of the rock, calibrated through thermodynamic experiments. Specifically, in implementation, this correction relationship can be customized in the multi-physics field coupling and expansion function, inputting the experimentally measured parameters and considering the influence of temperature on seepage characteristics.

[0109] Couple the temperature field with the fluid-solid coupling system through the energy conservation equation to achieve full coupling of seepage-deformation-temperature. The governing equations include:

[0110] ;

[0111] Among them, is the equivalent heat capacity of the rock and the fluid; is the equivalent thermal conductivity; is the fluid convective heat transfer term; is the heat source term converted from the mechanical work of solid deformation.

[0112] Based on the above-established full coupling mechanism of seepage-deformation-temperature: Temperature affects the seepage field by influencing the fluid viscosity, the pore pressure in the seepage field affects the deformation field through the effective stress, and the heat source generated by the deformation field and the seepage velocity are fed back to the temperature field through the energy equation. Specifically, in implementation, the software post-processing function can be used to analyze the contour maps of each field variable and the curves of the physical quantities at the monitoring points changing with time to verify the accuracy of the coupling mechanism and the effectiveness of the model.

[0113] S3. Calculate the stiffness of the mined vertical pile foundation, and correct the stiffness of the mined vertical pile foundation based on the factors such as soil compaction effect and negative skin friction, and apply the corrected stiffness of the mined vertical pile foundation to the finite element three-dimensional foundation calculation model;

[0114] In this step, the calculation of the initial stiffness of the mined vertical pile foundation is based on the pile foundation force and displacement , and the pile foundation force and displacement are calculated through the theoretical load and the elastic foundation model:

[0115] ;

[0116] Among them, is the unit weight of overburden soil, is the thickness of overburden soil, is the cross-sectional area of the pile, is the self-weight of the structure, is the live load, is the coefficient of subgrade reaction, is the pile length, is the flexural stiffness of the pile. Specifically, parameters are obtained from the geotechnical engineering investigation report and input into the software to calculate the pile foundation force and displacement, thereby providing data for calculating the initial stiffness of the pile foundation.

[0117] After obtaining the initial stiffness, it is corrected through a multi-factor correction formula:

[0118] ;

[0119] Among them, is the initial stiffness, is the pile material hardening model, is the pile-soil contact stiffness. Specifically, after obtaining the initial stiffness, correction parameters are obtained from the material performance test report and the research data on pile-soil interaction, and input into the software to calculate the corrected pile foundation stiffness, improving the calculation accuracy.

[0120] S4. Divide the mined tunneling construction into multiple stages, simulate the processes of stratum unloading, support structure construction, and precipitation-induced coupled hydro-mechanical behavior of soil and water, calculate the structural stress, deformation, and stratum displacement using the incremental method, and analyze the time-dependent behavior of the support structure and the influence of different excavation methods on stratum disturbance;

[0121] In this step, when simulating the construction process, the excavation is divided into multiple stages. According to the construction organization design plan, the excavation and support steps of each stage are defined in detail, and the corresponding units are activated or disabled sequentially in the model. By reasonably setting the unit activation time and stiffness change parameters, the mechanical state changes of the soil and structure during the construction process are simulated.

[0122] The incremental method is used to calculate the structural stress, strain, and stratum displacement during the construction process simulation. The stress increment formula is:

[0123] ;

[0124] Among them, is the stress increment at the stage, is the elastic stiffness matrix (reflecting the relationship related to elastic strain energy), is the strain increment at the stage.

[0125] During the simulation of the processes of stratum unloading, support structure construction, and precipitation-induced coupled hydro-mechanical behavior of soil and water, the time step is dynamically adjusted and satisfies:

[0126] ;

[0127] Among them, is a constant, is the characteristic length, is the elastic modulus, is the density.

[0128] Specifically, the characteristic length is obtained from the engineering design data, and parameters such as the elastic modulus and density are obtained from the material property report. The parameters and constants are input in the software calculation control parameter settings, and the software automatically calculates and dynamically adjusts the time step to balance the calculation accuracy and efficiency.

[0129] In addition, in this step, the mechanical property change of the support structure over time is also considered. The elastic modulus of the support structure changes over time as follows:

[0130] ;

[0131] where, is the initial elastic modulus, is the attenuation coefficient.

[0132] Specifically, in the software time-varying property setting of the material, parameters such as the initial elastic modulus and attenuation coefficient are input for the support structure, and the software updates the elastic modulus of the support structure in real time to simulate its mechanical property evolution.

[0133] In addition, the present invention also considers the influence of different excavation methods (such as the bench method, CD method, CRD method), and applies the corresponding equivalent loads in the model. Specifically, in the software construction simulation setting, for different excavation methods, according to their mechanical characteristics and construction steps, the magnitude, direction and acting position of the equivalent loads are analyzed and determined, and input into the software to simulate the influence of different excavation methods on the stratum and structure, and assist in the comparison and optimization of engineering schemes.

[0134] S5. Through finite element iterative solution, the structural response is obtained to evaluate the influence of the undercut excavation on the existing subway station.

[0135] In this step, through finite element iterative solution, iterative methods such as the Newton - Raphson method can be used to solve the nonlinear equations caused by material nonlinearity and fluid-structure coupling. The solution is iteratively updated in each construction stage to adapt to the change of mesh configuration and time-dependent material properties, and the convergence criterion based on the residual force or displacement is applied to ensure the convergence of the model calculation, so as to obtain the accurate structural response and stratum displacement.

[0136] Embodiment

[0137] This embodiment takes the method of analyzing the impact of the mined - tunneling under - crossing on the existing subway station as implemented on the MIDAS GTS software as an example. In this embodiment, first, by defining the geometric shapes, material properties, and section parameters of the structure and the stratum, combined with the adaptive mesh - generation technology, the key areas are discretized with refined meshes to construct a three - dimensional finite - element basic calculation model. Specifically, the stress - gradient tensor calculation formula is used to dynamically adjust the mesh density, and local densification is implemented in the area adjacent to the mined tunnel and the existing station, significantly improving the model accuracy. On this basis, a porous - medium seepage model is introduced, and the fluid - solid coupling control equation is established based on the Biot consolidation theory. The steady - state seepage equation is discretized by the finite - volume method, and the permeability tensor is corrected according to the fault attitude parameters to accurately represent the guiding effect of geological structures on the seepage path. In addition, the full coupling of seepage - deformation - temperature is realized through the energy - conservation equation, comprehensively considering the multi - physical - field interaction effects of groundwater flow, stratum deformation, and temperature field.

[0138] In terms of the construction - process simulation, the mined - tunneling construction is subdivided into multiple stages for dynamic analysis. For each stage, the excavation of the soil mass and the installation of the support structure are simulated by activating / deactivating elements, and the stress increment is calculated by the incremental method, which is based on the mathematical relationship between elastic strain energy and strain increment, and the internal force of the structure and the stratum displacement are gradually updated. At the same time, considering the time - dependent effect of the support structure, its mechanical parameters are dynamically corrected by the time - varying formula of the elastic modulus, and equivalent loads are applied for different construction methods to truly reflect the construction disturbance effect. By dynamically adjusting the time step, an optimal balance is achieved between computational efficiency and accuracy.

[0139] Finally, the Newton - Raphson iteration method is used to solve the non - linear equations, the convergence criterion based on the residual force or displacement threshold is set, and the efficient solution of multi - field coupling is realized in combination with the MIDAS GTS software. The calculation results are analyzed through the monitoring - point curves and nephograms to accurately evaluate the impact of the construction on the displacement, settlement, and stability of the existing station.

[0140] The specific implementation process is as follows:

[0141] 1. Construct a three - dimensional finite - element basic calculation model:

[0142] The implementation of this process includes: opening the MIDAS GTS software, entering the geometric modeling module, accurately drawing the geometries of the structure and the strata according to the engineering drawings, and detailedly inputting information such as the dimensions and positions of each part. Next, in the material property setting window, according to the material test reports, accurately set parameters such as the elastic modulus, Poisson's ratio, and density for different structural and stratum materials. Then, switch to the boundary condition setting module, reasonably set fixed boundaries and free boundaries to simulate the actual boundary constraint conditions, and at the same time add external loads, including in-situ stress, the frictional load between the subway station and the strata, and the additional load generated by construction disturbances. Finally, use the mesh generation function, select the adaptive mesh generation method, and customarily input the derived stress gradient tensor calculation formula and substitute it into the calculation, automatically adjust the mesh density, and refine key areas such as the vicinity of the mined tunnel and the existing subway station to complete the construction of the finite element three-dimensional basic calculation model.

[0143] In an exemplary implementation, the more specific implementation content includes:

[0144] When establishing the finite element basic model in the MIDAS GTS software, set the sandy soil layer part specifically as follows:

[0145] On the material constitutive model selection interface, select the Mohr - Coulomb model. Then, according to the detailed geological exploration report, obtain the cohesion and the internal friction angle and other parameters of the sandy soil layer. Accurately input the above parameters in the model parameter input column, and customarily input the derived mechanical constitutive model formula of the sandy soil layer , and during the subsequent calculation process, accurately simulate the mechanical responses of the sandy soil layer under different stress states, including the calculation of stress, strain, and deformation. This can more realistically reflect the changes in the mechanical properties of the sandy soil layer during the mined construction process and ensure the accuracy of the overall model.

[0146] In the boundary condition setting module of the MIDAS GTS software, the boundary conditions of the finite element foundation model are carefully set. Specifically: For fixed boundaries, select the corresponding constraint type to constrain the displacement degrees of freedom of the model boundary in specific directions, simulating the constraint effect of the bedrock on the structure in actual engineering, restricting the displacement of the structure in certain directions. For example, at the bottom boundary, the vertical displacement is constrained to simulate the support of the stratum to the structure. For free boundaries, ensure that the settings conform to the actual situation and allow the structure to deform freely at this boundary according to the actual stress and deformation conditions. In the load addition function area, various load factors are comprehensively considered. When adding external loads, according to the force analysis of the actual project, accurately input the magnitude, direction, and acting position of the load; for in-situ stress, calculate and input it based on the principles of geomechanics and in-situ stress test data; consider the friction load between the subway station and the stratum, and reasonably calculate and input this load according to the contact situation between the station structure and the stratum and the value range of the relevant friction coefficient; for the additional load caused by construction disturbance, estimate and add it in combination with the construction technology and on-site monitoring data. Through these operations, ensure that the stress state of the model truly reflects the actual engineering situation and improve the reliability of the model calculation results.

[0147] When performing mesh division, select the adaptive mesh division option in the mesh division function. In its parameter setting area, customarily input the derived stress gradient tensor calculation formula. Perform the operation. The software automatically calculates the stress gradient of the entire model domain and identifies key areas where the stress changes significantly, such as the adjacent parts of the mined tunnel and the existing subway station. For these key areas, the software automatically refines the mesh according to the set rules, increasing the number of elements and making the mesh size smaller; while in the areas where the stress changes relatively gently, appropriately increase the mesh size and reduce the number of elements. In this way, while ensuring the calculation accuracy, effectively control the calculation amount and improve the calculation efficiency.

[0148] 2. Multi-physical field coupling model considering the full coupling effect of seepage-deformation-temperature:

[0149] The implementation of this process includes: In the seepage analysis module of MIDAS GTS, create a stratum seepage model based on the porous medium theory. According to the on-site geological exploration and test data, accurately input parameters such as the stratum permeability in the model parameter settings. Use the Biot consolidation theory built into the software to describe the interaction between soil deformation and seepage. In the construction stage analysis function, for each construction stage, consider the influence of stratum deformation on the seepage path and permeability, and achieve an accurate simulation of the coupling process of groundwater flow and stratum deformation in each construction stage.

[0150] In an exemplary implementation scheme, the more specific implementation content includes:

[0151] Enter the seepage analysis module in the MIDAS GTS software and select to build a seepage model based on the porous medium theory. During the model construction process, according to the on-site geological exploration data, including information such as the lithology and pore structure of the strata, as well as the permeability coefficient data obtained from pumping tests and water pressure tests, accurately input relevant parameters such as the formation permeability in the formation permeability parameter setting interface of the software. The accurate setting of these parameters is the key for the model to accurately reflect the seepage characteristics of the formation, providing a reliable data basis for subsequent consideration of the fluid-structure interaction effect and analysis of the impact of groundwater on the project. For example, for formations with different lithologies, according to the determined differences in permeability coefficients from tests, accurately set the corresponding permeability parameters to make the seepage model more in line with the actual formation situation.

[0152] In the seepage model setting section of the MIDAS GTS software, custom input the steady-state seepage equation derived from the coupling of the anisotropic Darcy's law and the continuity equation. Discretize this seepage equation using the finite volume method. In the parameter settings during the discretization process, customize the discretization form of the control unit. Accurately set parameters such as the area calculation method of the surface (e.g., select the appropriate area calculation formula according to the element geometry), the distance measurement method (clarify the measurement rules for the distance from the surface to the element center), and the calculation and assignment of the equivalent permeability tensor. By correctly setting these parameters, the seepage equation can be accurately solved to obtain calculation results related to seepage such as the head distribution in the formation, providing data support for subsequent analysis of groundwater flow patterns and fluid-structure interaction.

[0153] In the multi-physics coupling setting module of the MIDAS GTS software, couple the seepage equation and the solid deformation control equation according to the mixture theory. In the coupling parameter setting interface, custom input the control equation of the fluid-structure coupling system derived according to the physical and mechanical properties of the rock and soil mass in the actual project. , The additional strain rate term in the seepage equation reflects the two-way coupling effect between fluid seepage and solid deformation. By accurately setting these parameters, simulate the interaction between the two during the fluid-structure coupling process, and more realistically reflect the mechanical relationship between groundwater, the formation, and the structure in underground engineering.

[0154] In the seepage model parameter adjustment function of the MIDAS GTS software, according to the attitude parameters (dip direction, dip angle, density) of faults and joints in the formation, customize the formula. The seepage tensor is corrected. Parameters are obtained and the corrected seepage tensor is automatically calculated using a formula, and it is applied to the fluid-structure interaction equation, so as to accurately characterize the guiding effect of geological structures on the seepage path and make the model more in line with the seepage conditions under actual geological conditions. For example, in a formation area with a fault, by correcting the seepage tensor, the seepage changes of groundwater near the fault and its influence on the surrounding formations and structures can be more accurately simulated.

[0155] In the multi-physics coupling extension function of the MIDAS GTS software, the corrected relationship between the temperature field and permeability derived from custom input is used. In the coupling setting interface of the temperature field and seepage field, the coefficient of thermal expansion of the rock measured by thermodynamic experiments is input. parameters such as the fluid viscosity at different temperatures etc. During the calculation process, according to this corrected relationship, the permeability is adjusted in real time dynamically, fully considering the influence of temperature changes on seepage characteristics, making the seepage calculation results more accurate. For example, when calculating underground engineering in some areas with geothermal energy, considering the influence of temperature on permeability can more accurately analyze the flow of groundwater.

[0156] In the advanced multi-physics coupling module of the MIDAS GTS software, the temperature field and the fluid-structure coupling system are coupled through the energy conservation equation. In the control equation setting interface, the fully coupled control equation of seepage-deformation-temperature derived from custom input is used. To achieve an accurate simulation of the full coupling of seepage-deformation-temperature, comprehensively considering the interaction between multi-physics fields. During the setting process, the equivalent heat capacities of the rock and fluid the equivalent thermal conductivity the fluid convective heat transfer term the heat source term converted from the mechanical work of solid deformation and other parameters are accurately input to simulate the mutual influence between the temperature field, seepage field and deformation field, providing a more comprehensive method for the analysis of underground engineering under complex geological conditions.

[0157] After completing the full coupling simulation of seepage-deformation-temperature in the MIDAS GTS software, the results are analyzed using the post-processing function of the software. View the variable contour maps of the temperature field, seepage field and deformation field to intuitively master the distribution of each field. For example, judge the high and low temperature distribution from the temperature contour map and the seepage direction from the seepage field contour map. Set monitoring points at key positions to obtain the curves of physical quantities such as temperature, pore water pressure and displacement changing with time. When analyzing the influence of temperature on the seepage field, the formula derived from custom input is used. Compare the seepage field data when the temperature changes to see the seepage changes caused by the change of permeability. To study the influence of the pore pressure in the seepage field on the deformation field, with the help of the fluid-structure interaction equation, analyze the stress-strain and displacement changes in the deformation field when the pore water pressure changes.

[0158] 3. Accurately calculate the stiffness of the vertical bored piles:

[0159] The implementation of this process includes: in the MIDAS GTS software, using the formula editor or custom calculation function, custom input the formula derived from the pile force and displacement calculated through the theoretical load and elastic foundation model , obtain the soil overburden unit weight from the engineering investigation report and structural design document , the soil overburden thickness , the pile cross-sectional area , the self-weight of the structure , the live load , the coefficient of subgrade reaction , the pile length , the flexural stiffness EI of the pile and other relevant parameters and input them to calculate the initial stiffness of the pile foundation. Considering influencing factors such as soil compaction effect and negative skin friction, in the parameter correction function of the model, use the multi-factor correction formula , determine the pile material hardening model , the pile-soil contact stiffness and other correction parameters, correct the initial stiffness, and apply the corrected stiffness to the position of the pile foundation stiffness parameter in the foundation calculation model.

[0160] In an exemplary implementation, the more specific implementation content includes:

[0161] In the calculation and analysis function module of the MIDAS GTS software, using the established theoretical load and elastic foundation model, custom input the derived formula to calculate the pile force and displacement and obtain the calculation results of the pile force and displacement.

[0162] In the stiffness calculation and correction function module of the MIDAS GTS software, custom input the derived multi-factor correction formula to calculate the corrected stiffness of the pile foundation. First, obtain the initial stiffness calculated previously , then, obtain the relevant parameters of the pile material hardening model from the pile material performance test report, and obtain the relevant parameters of the pile-soil contact stiffness from the pile-soil interaction research data and on-site test data. Input these parameters into the correction parameter setting area of the software, and the software automatically calculates according to this formula to obtain the corrected stiffness of the pile foundation, improving the accuracy of the pile foundation stiffness calculation and making it more in line with the mechanical characteristics of the pile foundation in actual projects.

[0163] 4. Simulate the construction process:

[0164] The implementation of this process includes: in the construction stage analysis module of MIDAS GTS, according to the detailed construction organization design plan, the excavation is divided into multiple stages. In the setting of each stage, the corresponding excavation and support steps are clarified, and the process of soil excavation and the construction of the support structure are simulated by activating or disabling the corresponding elements. When activating or disabling the elements, according to the construction sequence and technological requirements, parameters such as the activation time and stiffness change of the elements are reasonably set to truly reflect the changes in the mechanical states of the soil and the structure during the construction process. The incremental method is used to calculate the internal force, deformation and ground displacement of the structure. In the calculation method setting, the derived stress increment formula is customarily input , and parameters such as the calculation method of elastic strain energy (such as selecting a suitable elastic constitutive model to determine the elastic stiffness matrix ) and the solution method of strain increment are set. According to the principle of the incremental method, the software gradually calculates the increments of stress, strain and ground displacement in each construction stage. At the same time, considering the time-dependent characteristics of the support structure, in the setting of material time-varying characteristics, for the support structure, the derived formula for the change of elastic modulus with time is customarily input , and the initial elastic modulus is obtained from the material performance research report of the support structure and engineering experience data and the attenuation coefficient and other parameters are input into the software material time-varying parameter setting column, and the software dynamically updates the elastic modulus of the support structure during the calculation process. In addition, considering the influence of different excavation methods on ground disturbance, in the construction simulation setting, for different excavation methods (such as the bench method, CD method, CRD method), according to their mechanical characteristics and construction steps, corresponding equivalent loads are applied in the model to simulate. In the equivalent load setting interface, according to engineering experience and theoretical analysis, parameters such as the magnitude, direction and action position of the equivalent loads corresponding to different excavation methods are determined and input into the software.

[0165] In an exemplary implementation scheme, the more specific implementation content includes:

[0166] In the construction stage analysis module of MIDAS GTS software, according to the construction organization design plan, the excavation is divided into multiple stages. In the setting window of each stage, the corresponding excavation and support steps are defined in detail. For example, for a certain stage, it is set to first excavate a certain volume of soil mass and then construct the corresponding support structure. During the simulation process, the excavation of the soil mass and the construction of the support structure are simulated by activating or disabling the corresponding elements. When activating the elements, according to the actual construction sequence and technological requirements, the activation time of the elements is reasonably set to ensure the accuracy of the simulated construction sequence; for the support structure elements, the stiffness change parameters also need to be set to simulate the change of the mechanical properties of the support structure during the construction process. Through these settings, the mechanical states of the soil mass and the structure during the construction process are truly reflected as they change over time, providing accurate simulation data for analyzing the impact of construction on the existing subway station.

[0167] In the calculation method setting of MIDAS GTS software, the incremental method is selected to calculate the structural stress, strain and formation displacement. On the interface for setting the incremental method calculation parameters, the derived stress increment formula is customarily input for parameter setting. First, determine the calculation method of the elastic strain energy and select a suitable model according to the material properties of the actual project; then, set the solution method of the strain increment to ensure the accuracy and stability of the calculation. According to the principle of the incremental method, the increments of stress, strain and formation displacement are gradually calculated in each construction stage, and by accumulating these increments, the results of stress, strain and formation displacement in each construction stage are obtained. When selecting the elastic strain energy calculation model, refer to the characteristics such as the stress-strain curve of the material for selection to ensure that the calculation results conform to the actual mechanical behavior of the material.

[0168] In the setting of the calculation control parameters of MIDAS GTS software, the derived formula is customarily input for the dynamic adjustment of the time step. The characteristic length can be obtained from the engineering design data , the elastic modulus can be obtained from the material performance report and the density and other parameters are input. According to this formula, the time step is automatically calculated and dynamically adjusted. During the calculation process, when the mechanical response of the structure or formation changes greatly, the time step is automatically reduced to improve the calculation accuracy; when the mechanical response changes little, the time step is appropriately increased to improve the calculation efficiency, ensuring the balance between the reliability of the calculation results and the calculation efficiency. For example, at the initial stage of the excavation of the mined tunnel, the formation stress changes violently, and the software automatically reduces the time step to finely capture the mechanical response; as the construction progresses and the formation gradually stabilizes, the time step is appropriately increased to speed up the calculation.

[0169] In the time-varying property settings of materials in the MIDAS GTS software, consider the change in mechanical properties of the support structure over time. In the material parameter setting interface of the support structure, custom-enter the formula for the change of the elastic modulus of the support structure over time for setting. Obtain the initial elastic modulus and attenuation coefficient and other parameters from the research report on the material properties of the support structure and similar engineering experience data, and input these parameters into the time-varying parameter setting column of the software. During the calculation process of the software, the elastic modulus of the support structure is updated in real time and dynamically according to this formula, accurately simulating the mechanical property evolution of the support structure during the construction process due to factors such as material aging and aging. For example, for steel supports, determine the attenuation coefficient based on their material properties and past engineering data, and simulate the decrease in elastic modulus during the long-term construction process to more realistically reflect the actual mechanical state of the support structure.

[0170] In the construction simulation settings of the MIDAS GTS software, simulate the influence of different excavation methods (such as the bench method, CD method, CRD method). When simulating different excavation methods, according to their mechanical characteristics and construction steps, apply corresponding equivalent loads in the model for simulation. Taking the bench method as an example, analyze its influence on the stratum and structure according to the excavation sequence and soil unloading characteristics of the bench method, and determine the magnitude, direction, and acting position of the equivalent load. In the equivalent load setting interface, input these parameters into the software, and the software simulates the mechanical effects on the stratum and structure during the construction process of the bench method by applying this equivalent load. Similarly, for the CD method and CRD method, determine and apply the equivalent load in a similar way to simulate the influence of different excavation methods on the stratum and structure, providing a basis for the comparison and optimization of engineering plans. For example, compare the differences in stratum displacement and structural stress generated by the bench method and the CD method under the same geological conditions and engineering requirements to assist in selecting a more suitable construction method.

[0171] 5. Solve by finite element iteration:

[0172] The implementation of this process includes: performing finite element iteration and solution in the MIDAS GTS software. In the solution settings, for the non-linear equations caused by material non-linearity and fluid-structure coupling, set the convergence criterion based on the residual force or displacement. In each construction stage, the software iteratively updates the solution to adapt to the changes in mesh configuration and time-dependent material properties, ensuring the convergence of the model calculation, so as to obtain an accurate structural response to evaluate the impact of the underground excavation under the existing subway station.

[0173] In an exemplary implementation scheme, the more specific implementation content includes:

[0174] In the MIDAS GTS software, iterative methods such as the Newton - Raphson method are selected for finite - element iterative solution. In the solution settings dialog box, for the non - linear equations caused by material non - linearity and fluid - structure interaction, convergence criteria based on the residual force or displacement are set. For example, when a certain component of the residual force or a certain component of the displacement is less than a specific threshold (such as ), the calculation is considered to have converged. During the calculation process of each construction stage, the software continuously iterates and updates the solution according to the selected iterative method to adapt to changes in the mesh configuration (such as mesh deformation caused by soil excavation and the construction of the support structure during the construction process) and time - dependent material properties (such as the change of the elastic modulus of the support structure over time). Through continuous iteration, the convergence of the model calculation is ensured, so as to obtain accurate structural response and formation displacement results.

[0175] Based on the description of the above embodiments, the present invention is closely combined with the actual engineering situation during the modeling and analysis process, fully considering the coupling effect of various physical factors and the dynamic changes during the construction process. The core advantages are reflected in three aspects:

[0176] First, through the fluid - structure coupling model and the fully coupled mechanism of seepage - deformation - temperature, the limitations of traditional methods in simulating the action of groundwater, spatio - temporal effects, and multi - physical - field interaction are broken through.

[0177] Second, by using adaptive mesh generation and the incremental method for dynamic simulation, the artificial modeling error is significantly reduced, and the efficient simulation of complex construction processes is realized.

[0178] Third, only by moderately modifying the corresponding parameters and construction - stage simulations, the adaptability of the model can be quickly adjusted, significantly enhancing the flexibility and application scope of the model.

[0179] Therefore, the present invention effectively solves the problems of complex multi - physical - field coupling, difficult simulation of the construction process, and hard to balance calculation accuracy and efficiency in the analysis of the influence of underground excavation under an existing subway station, providing strong technical support for the design, construction, and safety assessment of related projects.

[0180] Finally, it should be noted that the above embodiments are only preferred embodiments and are not intended to limit the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the spirit and scope protected by the claims of the present invention, several modifications, equivalent replacements, improvements, etc. should all be included within the protection scope of the present invention.

Claims

1. A method for analyzing the impact of underground tunneling on existing subway stations, characterized in that: The following steps are involved: S1. Construct a finite element three-dimensional basic calculation model by defining the geometry and material properties of the structure and strata, setting boundary conditions and external loads, and performing meshing; S2. Based on the finite element three-dimensional basic calculation model, a multi-physics field coupling model considering the full coupling effect of seepage-deformation-temperature is constructed; S3. Calculate the vertical pile foundation stiffness of the dark excavation, and modify the vertical pile foundation stiffness of the dark excavation based on the influence factors of soil squeezing effect and negative friction resistance, and apply the modified vertical pile foundation stiffness of the dark excavation to the finite element three-dimensional foundation calculation model; S4. The underground excavation construction is divided into multiple stages to simulate the process of ground unloading, support structure construction and precipitation water-soil flow-solid coupling. The structural stress, deformation and ground displacement are calculated using the incremental method, and the timeliness of the support structure and the influence of different excavation methods on ground disturbance are analyzed. S5. Obtain structural response through finite element iteration and evaluate the impact of underground tunneling on existing subway stations.

2. The method for analyzing the impact of underground excavation on existing subway stations as claimed in claim 1 is characterized in that: In step S1, when constructing the finite element three-dimensional basic calculation model, adaptive meshing is used to adjust the mesh density according to the stress gradient, wherein the stress gradient tensor calculation formula is: ； in, are the stress tensor components, are the coordinate components, is a unit vector; The global stress gradient of the model is calculated using this formula. The mesh is refined in the area adjacent to the dark tunnel and the existing subway station, and the mesh size is increased in the area where the stress changes slowly.

3. The method for analyzing the impact of underground excavation on existing subway stations as claimed in claim 1 is characterized in that: In step S1, the constructed finite element three-dimensional foundation calculation model includes layered modeling of strata, and different strata adopt different constitutive models; the finite element three-dimensional foundation calculation model is defined with boundary conditions, including fixed boundaries and free boundaries, and takes into account external loads, ground stress, friction between the subway station and the strata, and additional loads caused by construction disturbances; the fixed boundaries limit the displacement freedom in the boundary direction of the model to simulate bedrock constraints; the free boundaries allow the structure to deform according to actual conditions.

4. The method for analyzing the impact of underground excavation on existing subway stations as claimed in claim 1 is characterized in that: In step S2, a multi-physics coupling model considering the full coupling effect of seepage, deformation and temperature is constructed, including: A seepage model is established based on porous media theory. The seepage equation is coupled with the solid deformation control equation according to the mixture theory. The temperature field and the fluid-solid coupling system are coupled through the energy conservation equation, thus constructing a multi-physics field coupling model that considers the full coupling effect of seepage, deformation and temperature. The control equation of the seepage model is the steady-state seepage equation coupled with the anisotropic Darcy's law and the continuity equation: ； in, is the permeability tensor, is the water head value.

5. The method for analyzing the impact of underground excavation on existing subway stations as claimed in claim 4 is characterized in that: The seepage equation and the solid deformation control equation are coupled through the mixture theory. The control equation of the coupled fluid-solid coupling system is: ， ； in, is the effective stress tensor, is the displacement component, is the body force component, is the density of water, is the porosity, is the seepage velocity; The temperature field and the fluid-solid coupling system are coupled by the energy conservation equation to construct a multi-physics coupling model that considers the full coupling effect of seepage, deformation and temperature. The control equation is: ； in, is the equivalent heat capacity of rock and fluid; is the equivalent thermal conductivity; is the fluid convection heat transfer term; is the heat source term converted from mechanical work of solid deformation; T represents temperature.

6. The method for analyzing the impact of underground excavation on existing subway stations as claimed in claim 5, characterized in that: When building a multi-physics coupling model that considers the full coupling effects of seepage, deformation and temperature, it also includes: According to the occurrence parameters of faults and joints in the formation, the permeability tensor is modified: ； in, is the matrix permeability tensor; For the The permeability increment of the strip fault; is the structural influence attenuation coefficient, For the The strike angle of the fault, n is the number of faults in the formation; the corrected tensor Used in fluid-solid coupling equations to characterize the guiding effect of geological structures on seepage paths; Introducing the correction relationship between temperature field and permeability: ； in, For temperature The permeability under is the initial permeability, For temperature The fluid viscosity under is the fluid viscosity at the reference temperature, is the thermal expansion coefficient of rock, calibrated through thermodynamic experiments.

7. The method for analyzing the impact of underground excavation on existing subway stations as claimed in claim 1 is characterized in that: In step S3, the method for calculating the stiffness of the concealed excavation vertical pile foundation is: Calculation of pile forces using theoretical loads and elastic foundation models With displacement : ； in, It is heavy soil covering; is the thickness of the covering soil; is the cross-sectional area of ​​the pile; For the deadweight of the structure; is the live load; is the foundation soil reaction coefficient; is the pile length; is the bending stiffness of the pile; Based on pile force With displacement , calculate the initial stiffness of the concealed vertical pile foundation.

8. The method for analyzing the impact of underground excavation on existing subway stations as claimed in claim 7 is characterized in that: In step S3, the vertical pile foundation stiffness of the dark excavation is corrected based on the soil squeezing effect and negative friction resistance, including: ； in, is the initial stiffness of the underground vertical pile foundation, For the hardening model of pile material, is the pile-soil contact stiffness.

9. The method for analyzing the impact of underground excavation on existing subway stations as claimed in claim 1, characterized in that: In step S4, the calculation of structural stress, strain and formation displacement using the incremental method includes: ； in, For the The stress increment of the stage, is the elastic stiffness matrix, For the The strain increment of the stage.

10. The method for analyzing the impact of underground excavation on an existing subway station as claimed in claim 9, characterized in that: In step S4, the time step is dynamically adjusted during the simulation of ground unloading, support structure construction, and precipitation soil-water flow-solid coupling. , and satisfy: ； in, is a constant, is the characteristic length, is the elastic modulus, is the density.

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