A method for analyzing the influence of mined tunneling under existing subway stations

Abstract

The present invention relates to underground engineering construction design technology, which discloses a method for analyzing the impact of underground excavation on existing subway stations, thereby improving the efficiency and accuracy of the analysis of the impact of underground excavation on existing subway stations. The method includes: defining the geometric shape and material properties of the structure and stratum, setting boundary conditions and external loads, and performing grid division to construct a finite element three-dimensional foundation calculation model; constructing a multi-physics field coupling model of the full coupling effect of seepage-deformation-temperature based on theories such as porous media; calculating the stiffness of the underground vertical pile foundation, and correcting the stiffness of the underground vertical pile foundation based on the influencing factors of soil squeezing effect and negative friction resistance; subdividing the underground excavation construction into multiple stages, using the incremental method to calculate the structural stress, deformation and stratum displacement, and analyzing the timeliness of the support structure and the impact of different excavation methods on stratum disturbance; obtaining the structural response through finite element iterative solution, and evaluating the impact of underground excavation on existing subway stations.

Description

Technical Field

[0001] The present invention relates to underground engineering construction design technology, and in particular to a method for analyzing the impact of underground excavation on existing subway stations. Background Art

[0002] In underground engineering construction, tunneling has become a key method for constructing infrastructure such as subways and tunnels. Due to its minimal environmental impact, high construction flexibility, and adaptability to complex geological conditions, tunneling technology is widely used in urban rail transit and other underground projects. During tunneling, the rationality of the construction methods and processes directly impacts the safety and stability of existing structures.

[0003] Tunneling construction typically involves excavation beneath or near existing subway stations. Ground deformation, stress redistribution, and disturbance to existing structures during construction can impact the structural safety and operational safety of existing stations. Therefore, accurately assessing the impact of tunneling on existing stations is crucial for optimizing construction plans and ensuring operational safety.

[0004] Currently, numerical simulation methods based on finite element analysis are commonly used to analyze the impact of underground tunnel construction on existing subway stations. This method artificially constructs a three-dimensional numerical model to simulate the complex mechanical behavior of ground deformation, the stress on the existing station structure, and the interaction between the construction process during underground tunnel construction. Its specific implementation is as follows:

[0005] 1. Manual definition and modeling

[0006] During this process, researchers manually defined various parameters of the numerical model based on the actual requirements of the underground tunnel project, including the geometry of the existing station structure, material properties, and the interaction between the strata and the structure. These parameters were typically set based on engineering experience, geological survey data, and design standards. The modeling process was completed using professional numerical simulation software and required multiple adjustments and verifications to ensure the model's rationality. The specific steps included:

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

[0008] (2) Setting the interaction relationship: Based on the physical and mechanical properties of the stratum, the interaction relationship between the stratum and the structure is set. For example, a spring unit is used to simulate the constraint of the stratum on the structure. The stiffness and other parameters of the spring unit are determined based on the physical and mechanical parameters of the stratum, such as the elastic modulus and Poisson's ratio.

[0009] (3) Determine boundary conditions: Set the model's boundary conditions and external loads, such as formation stress, groundwater pressure, and construction disturbance effects. Formation stress is determined based on the ground stress test results of geological surveys, and groundwater pressure is calculated based on the groundwater level depth and water density.

[0010] (4) Model calibration: Through multiple simulations and adjustments, the model parameters are optimized to ensure that the simulation results are consistent with engineering experience or existing data. For example, the model-calculated ground settlement results are compared with actual monitoring data from similar projects, and the model parameters are continuously adjusted until the deviation between the two is within an acceptable range.

[0011] 2. Segmented Discrete Model and Local Refinement

[0012] To improve model accuracy, the tunnel and existing station structures are typically discretized into multiple elements (such as beams, shells, or solids) to form a finite element model. For complex conditions, such as uneven strata or asymmetric loading, localized regions may be further refined to capture stress concentrations and deformation behavior. This improves model flexibility and accuracy, making it suitable for analyzing local stress characteristics and sensitive areas.

[0013] 3. Static and dynamic simulation analysis

[0014] Based on the constructed numerical model, researchers used finite element analysis tools to analyze the structural behavior of the existing station during the tunneling construction process. This included both static analysis (e.g., structural stability and ground deformation) and dynamic analysis (e.g., the effects of construction disturbance and ground consolidation). This analysis is often used to assess ground settlement, stress distribution in the existing station structure, and structural stability, assisting in engineering design and construction decision-making.

[0015] While existing finite element-based numerical simulations can simulate the impact of underground tunneling on existing subway stations to a certain extent, they have the following limitations:

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

[0017] Finite element analysis often uses a full-scale model, assuming that the impact of construction on the structure and ground is static and one-time. This model fails to dynamically reflect the gradual excavation, support, and structural stress changes during construction. This model ignores the temporal and spatial effects of the construction process, making it difficult to simulate the stress release and accumulated deformation of the ground during construction, as well as the dynamic response of the existing structure. For example, in actual construction, as excavation progresses, ground stress gradually releases, and structural stresses continuously change, but a full-scale model cannot accurately reflect this process.

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

[0019] (2) The boundary conditions are simple and the effect of groundwater is not considered.

[0020] Existing technologies are relatively simplistic in their boundary condition settings, typically considering only formation stress and external loads, while failing to fully account for the effects of groundwater. The presence of groundwater can significantly affect the mechanical properties of the formation and the stability of existing structures. This is particularly true during underground excavation, where groundwater flow can cause formation subsidence, deformation of existing structures, and even leakage. For example, during underground excavation in water-rich formations, groundwater seepage can alter the effective stress distribution in the formation, thereby affecting structural stability. However, existing models often overlook this factor.

[0021] Because the effect of groundwater is not taken into account, existing models may underestimate ground deformation and the stress on existing structures when analyzing the impact of underground tunnel construction on existing subway stations, resulting in a lack of targetedness and safety in design and construction plans.

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

[0023] Existing technologies often directly use complex three-dimensional finite element models during modeling without proper simplification. While high-precision models can capture more details, they also significantly increase computational complexity, lengthen calculation times, and make efficient adjustments and optimization difficult.

[0024] The complexity and lack of simplification of the model not only limits computational efficiency but also increases modeling difficulty and cost, making it difficult to meet the demands of rapid response and real-time monitoring in engineering practice. Furthermore, complex models are prone to human error during parameter setting and calibration, reducing the accuracy and reliability of the model.

[0025] In summary, existing approaches for analyzing the impact of underground tunneling on existing subway stations suffer from the following flaws: model construction relies heavily on manual labor and empirical judgment, failing to dynamically reflect the spatiotemporal effects of the construction process; the boundary conditions are simplistic and fail to fully account for the impact of groundwater on strata and structures; and the models are complex and unsimplified, resulting in high computational complexity and low efficiency. These flaws make existing methods difficult to meet the practical needs of rapid engineering decision-making and optimized design, highlighting their limitations in practical applications. Therefore, improvements in modeling and simulation technology are urgently needed to enhance 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 impact of underground excavation on existing subway stations, improve the efficiency and accuracy of the analysis of the impact of underground excavation on existing subway stations, and at the same time consider the influence of the settlement and 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:

[0028] A method for analyzing the impact of underground tunneling on an existing subway station includes the following steps:

[0029] S1. Construct a 3D finite element model by defining the geometry and material properties of the structure and strata, setting boundary conditions and external loads, and performing meshing.

[0030] S2. Based on the finite element three-dimensional basic calculation model, a multi-physics coupling model considering the full coupling effects of seepage, deformation, and temperature is constructed;

[0031] S3. Calculate the vertical pile foundation stiffness of the underground excavation, and modify it based on the soil squeezing effect and negative friction. Apply the modified vertical pile foundation stiffness to the finite element three-dimensional foundation calculation model.

[0032] S4. Divide the underground excavation construction into multiple stages, simulating the process of ground unloading, support structure construction, and water-soil-fluid-solid coupling during precipitation. Use the incremental method to calculate structural stress, deformation, and ground displacement, and analyze the timeliness of the support structure and the impact of different excavation methods on ground disturbance.

[0033] S5. Obtain structural responses through iterative finite element analysis and evaluate the impact of the underground tunnel on existing subway stations.

[0034] Furthermore, 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:

[0035] ;

[0036] in, are the stress tensor components, are coordinate components, is a unit vector;

[0037] This formula is used to calculate the global stress gradient of the model. The mesh is refined in the area adjacent to the underground tunnel and the existing subway station, and the mesh size is increased in areas with gentle stress changes.

[0038] Furthermore, 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.

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

[0040] 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 effects of seepage, deformation, and temperature.

[0041] The governing equation of the seepage model is the steady-state seepage equation coupled with the anisotropic Darcy law and the continuity equation:

[0042] ;

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

[0044] Furthermore, 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:

[0045] , ;

[0046] 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;

[0047] 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. Its control equation is:

[0048] ;

[0049] in, is the equivalent heat capacity of rock and fluid; is the equivalent heat transfer coefficient; is the fluid convection heat transfer term; is the heat source term converted from mechanical work of solid deformation; T represents temperature.

[0050] Furthermore, when constructing a multi-physics coupling model that considers the full coupling effects of seepage, deformation, and temperature, it also includes:

[0051] According to the occurrence parameters of faults and joints in the formation, the permeability tensor is modified:

[0052] ;

[0053] in, is the matrix permeability tensor; For the Permeability increment of the fault strip; 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;

[0054] Introducing the correction relationship between temperature field and permeability:

[0055] ;

[0056] in, Temperature The permeability under is the initial permeability, Temperature The fluid viscosity under is the fluid viscosity at the reference temperature, is the thermal expansion coefficient of rock, calibrated through thermodynamic experiments.

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

[0058] Calculation of pile foundation forces using theoretical loads and elastic foundation models and displacement :

[0059] ;

[0060] in, It is heavy soil covering; is the thickness of the cover soil; is the cross-sectional area of the pile; The weight of the structure; is the live load; is the foundation soil reaction coefficient; is the pile length; is the pile bending stiffness;

[0061] Based on pile foundation force and displacement , calculate the initial stiffness of the concealed vertical pile foundation.

[0062] Furthermore, in step S3, the stiffness of the underground vertical pile foundation is corrected based on the soil squeezing effect and negative friction resistance, including:

[0063] ;

[0064] in, is the initial stiffness of the underground vertical pile foundation, For the hardening model of pile material, is the pile-soil contact stiffness.

[0065] Furthermore, in step S4, calculating the structural stress, strain and formation displacement using the incremental method includes:

[0066] ;

[0067] in, For the The stress increment of the stage, is the elastic stiffness matrix, For the The strain increment of the stage.

[0068] Furthermore, 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:

[0069] ;

[0070] in, 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 time and space effects, dynamically simulate the construction process:

[0073] The present invention takes into account the gradual loading, stratum stress release, deformation accumulation and dynamic response of existing structures during the construction process. By dividing the construction process into multiple stages, the excavation, support and other operations in each stage are simulated, and the mechanical changes of the structure and stratum are tracked in real time, thereby more accurately predicting the impact of construction on existing subway stations and providing more reliable protection for construction safety.

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

[0075] The present invention introduces a fluid-solid coupling mechanical model, taking into account factors such as the groundwater seepage path and pore water pressure changes in the model, and then comprehensively considering the impact of groundwater flow on the mechanical properties of the formation and the stability of existing structures, thereby more accurately simulating formation settlement, structural deformation and leakage risks, and improving the accuracy and safety of the analysis.

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

[0077] The present invention introduces a calculation model for pile foundation settlement and deformation, taking into account the impact of pile foundation settlement and deformation on existing structures. In addition, it also considers the impact of factors such as the soil squeezing effect and negative friction during pile foundation construction on settlement. By comprehensively considering the impact of multiple factors on pile foundation settlement, more accurate data is provided for the structural safety assessment of subway stations.

[0078] (4) Simplify model construction and improve computational efficiency:

[0079] When constructing a finite element three-dimensional basic calculation model, the present invention adopts adaptive meshing technology to encrypt the mesh in key areas and appropriately enlarge the mesh size in non-key areas, thereby improving calculation efficiency while ensuring calculation accuracy.

[0080] In summary, the present invention improves the efficiency and accuracy of the analysis of the impact of underground excavation construction on existing subway stations, while taking into account 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 This is a flow chart of the method for analyzing the impact of underground excavation on existing subway stations in the present invention. DETAILED DESCRIPTION

[0082] The present invention aims to provide a method for analyzing the impact of underground excavation on existing subway stations, improve the efficiency and accuracy of the analysis of the impact of underground excavation on existing subway stations, and consider the influence of the settlement and 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. Its core ideas are: (1) The existing technology adopts a full-volume model, which cannot dynamically reflect the gradual excavation, support and structural stress changes during the construction process, and ignores the time and space effects 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 the excavation, support and other operations in each stage, and tracking the mechanical changes of the structure and stratum in real time, it can more accurately predict the impact of construction on existing subway stations and provide more reliable protection for construction safety. (2) The existing technology is relatively simple in setting boundary conditions and does not fully consider the impact of groundwater on the stability of the stratum and existing structures. To address this problem, the present invention introduces a fluid-solid coupling mechanical model, considers factors such as groundwater seepage path and pore water pressure changes in the model, and then comprehensively considers the impact of groundwater flow on the mechanical properties of the stratum and the stability of the existing structure, thereby more accurately simulating stratum settlement, structural deformation and leakage risk, and improving the accuracy and safety of the analysis. (3) In the existing technology, the impact of pile foundation settlement deformation on existing subway stations has not been fully considered, resulting in large deviations in the calculation results. To address this problem, the present invention introduces a calculation model for pile foundation settlement deformation, considers the impact of pile foundation settlement deformation on existing structures, and also considers the impact of factors such as soil squeezing effect and negative friction resistance during pile foundation construction on settlement. By comprehensively considering the impact of multiple factors on pile foundation settlement, more accurate data is provided for subway station structural safety assessment. (4) The existing technology uses a complex three-dimensional finite element model and does not reasonably simplify the model, resulting in high calculation complexity and low efficiency. To address this problem, the present invention adopts adaptive meshing technology when constructing the finite element three-dimensional basic calculation model, encrypts the mesh in key areas, and appropriately enlarges the mesh size in non-key areas, thereby improving calculation efficiency while ensuring calculation accuracy.

[0083] In specific implementation, the method flow for analyzing the impact of underground excavation on existing subway stations provided by the present invention can be found in Figure 1 , which includes the following implementation process:

[0084] S1. Construct a 3D finite element model by defining the geometry and material properties of the structure and strata, setting boundary conditions and external loads, and performing meshing.

[0085] In this step, the finite element basic calculation model includes layered modeling of strata, and different strata use different constitutive models. For example, the sand layer uses the Mohr-Coulomb model, and the mechanical constitutive model formula of the sand layer is:

[0086] ;

[0087] in, 、 The principal stress, For cohesion, is the internal friction angle. The parameters of the sand layer are obtained according to the geological survey report and substituted into the formula to accurately simulate the mechanical response of the sand layer.

[0088] Finite element foundation calculation models require appropriate boundary conditions, including fixed and free boundaries, and consider external loads, geostress, friction between the subway station and the ground, and additional loads caused by construction disturbances. Fixed boundaries restrict the model's displacement freedom in specific directions, simulating bedrock constraints; free boundaries allow the structure to deform according to actual conditions.

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

[0090] ;

[0091] in, are the stress tensor components, are coordinate components, This formula is used to calculate the global stress gradient of the model. The mesh is refined in key areas, such as those near the tunnel and existing subway stations, and the mesh size is appropriately increased in areas with gentle stress changes, improving calculation accuracy while controlling the amount of computation required.

[0092] S2. Based on the finite element three-dimensional basic calculation model, a multi-physics coupling model considering the full coupling effects of seepage, deformation, and temperature is constructed;

[0093] In this step, a seepage model is first established based on porous media theory, and Biot's consolidation theory is applied to describe soil deformation. The effects of faults and joints on the permeability tensor are then considered, and a modified model is developed. By incorporating the influence of the temperature field on permeability, a coupled analysis of the seepage, stress, and temperature fields is achieved, yielding an accurate fluid-solid coupling response.

[0094] The governing equation of the seepage model is the steady-state seepage equation coupled with the anisotropic Darcy law and the continuity equation:

[0095] ;

[0096] in, is the permeability tensor, is the water head value;

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

[0098] ;

[0099] in, For the surface The area, For the surface To the unit center distance, For the surface The equivalent permeability tensor of .

[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] in, is the effective stress tensor, is the displacement component, is the medium density, is the body force component, is the density of water, is the porosity, In practice, according to the actual physical and mechanical properties of the rock and soil, the parameters required for the control equation are customized in the multi-physics coupling setting module to simulate the fluid-solid coupling process.

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

[0104] ;

[0105] in, is the matrix permeability tensor; For the Permeability increment of faults / joints; is the structural influence attenuation coefficient, For the strike angle of a fault; modified tensor Used in fluid-solid coupling equations to characterize the guiding effect of geological structures on seepage paths.

[0106] Introducing the correction relationship between temperature field and permeability:

[0107] ;

[0108] in, Temperature The permeability under is the initial permeability, Temperature The fluid viscosity under is the fluid viscosity at the reference temperature, The thermal expansion coefficient of rock is calibrated through thermodynamic experiments. Specifically, this correction relationship can be customized in the Multiphysics Coupling extension by inputting experimentally determined parameters to account for the effect of temperature on seepage characteristics.

[0109] The temperature field and fluid-solid coupling system are coupled by the energy conservation equation to achieve full coupling of seepage, deformation and temperature. The control equations include:

[0110] ;

[0111] in, is the equivalent heat capacity of rock and fluid; is the equivalent heat transfer coefficient; is the fluid convection heat transfer term; It is the heat source term converted from mechanical work of solid deformation.

[0112] The coupling mechanism for the fully coupled seepage, deformation, and temperature established above is as follows: temperature affects the seepage field by influencing fluid viscosity, pore pressure in the seepage field influences the deformation field through effective stress, and the heat source and seepage velocity generated by the deformation field are fed back into the temperature field through the energy equation. Specifically, the software's post-processing capabilities can be used to analyze cloud plots of field variables and time-varying curves of physical quantities at monitoring points to verify the accuracy of the coupling mechanism and the effectiveness of the model.

[0113] S3. Calculate the vertical pile foundation stiffness of the underground excavation, and modify it based on the soil squeezing effect and negative friction. Apply the modified vertical pile foundation stiffness to the finite element three-dimensional foundation calculation model.

[0114] In this step, the calculation of the initial stiffness of the underground vertical pile foundation is based on the pile foundation force and displacement , and the pile foundation force and displacement Calculation using theoretical load and elastic foundation model:

[0115] ;

[0116] in, For heavy soil cover, is the thickness of the cover soil, is the cross-sectional area of the pile, The weight of the structure, For live load, is the foundation soil reaction coefficient, Pile length, The bending stiffness of the pile is obtained from the geotechnical engineering survey report and input into the software to calculate the pile foundation force and displacement, thus providing data for calculating the initial stiffness of the pile foundation.

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

[0118] ;

[0119] in, is the initial stiffness, For the hardening model of pile material, In practice, after obtaining the initial stiffness, correction parameters are obtained from material performance test reports and pile-soil interaction research data, and then input into the software to calculate the corrected pile foundation stiffness to improve calculation accuracy.

[0120] S4. Divide the underground excavation construction into multiple stages, simulating the process of ground unloading, support structure construction, and water-soil-fluid-solid coupling during precipitation. Use the incremental method to calculate structural stress, deformation, and ground displacement, and analyze the timeliness of the support structure and the impact of different excavation methods on ground 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. The corresponding units are activated or disabled in the model in sequence. By reasonably setting the unit activation time and stiffness change parameters, the changes in the soil and structural mechanical states during the construction process are simulated.

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

[0123] ;

[0124] in, For the The stress increment of the stage, is the elastic stiffness matrix (reflecting the elastic strain energy correlation), For the The strain increment of the stage.

[0125] Dynamically adjust the time step in the process of simulating ground unloading, support structure construction, and precipitation water-soil fluid-solid coupling , and satisfy:

[0126] ;

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

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

[0129] In addition, this step also considers the change of mechanical properties of the support structure over time. The elastic modulus of the support structure changes with time. Changes to:

[0130] ;

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

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

[0133] Furthermore, this invention considers the impact of different excavation methods (such as the step method, CD method, and CRD method) and applies corresponding equivalent loads to the model. Specifically, within the software's construction simulation settings, the equivalent load magnitude, direction, and location are determined based on the mechanical characteristics and construction steps of each excavation method. This data is then fed into the software to simulate the impact of different excavation methods on the ground and structure, assisting in the comparison and optimization of engineering solutions.

[0134] S5. Obtain structural responses through iterative finite element analysis and evaluate the impact of the underground tunnel on existing subway stations.

[0135] In this step, iterative methods such as the Newton-Raphson method can be used to solve the nonlinear equations caused by material nonlinearity and fluid-structure interaction through finite element iterative solution. The solution is iteratively updated during each construction stage to adapt to changes in mesh configuration and time-dependent material properties. Convergence criteria based on residual forces or displacements are applied to ensure the convergence of the model calculation, thereby obtaining accurate structural responses and formation displacements.

[0136] Example:

[0137] This embodiment takes the method of implementing the above-mentioned analysis of the impact of underground tunneling on existing subway stations on the MIDAS GTS software as an example. In this embodiment, first, by defining the geometric shape, material properties and cross-sectional parameters of the structure and stratum, the adaptive meshing technology is combined to perform fine mesh discretization on the key areas and construct a finite element three-dimensional basic calculation model. Specifically, the stress gradient tensor calculation formula is used to dynamically adjust the mesh density, and local encryption is implemented in the areas adjacent to the underground tunnel and the existing station, which significantly improves the accuracy of the model. On this basis, a porous media seepage model is introduced, and a 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 characterize the guiding effect of the geological structure on the seepage path. In addition, the full coupling of seepage, deformation and temperature is achieved through the energy conservation equation, and the multi-physical field interaction effects of groundwater flow, stratum deformation and temperature field are fully considered.

[0138] In terms of construction process simulation, the underground excavation process was divided into multiple stages for dynamic analysis. For each stage, soil excavation and support structure construction were simulated by activating / deactivating elements. Stress increments were calculated using an incremental method based on the mathematical relationship between elastic strain energy and strain increments, gradually updating the internal forces and ground displacements. Furthermore, considering the timeliness of the support structure, its mechanical parameters were dynamically modified using a time-varying elastic modulus formula. Equivalent loads were applied for different construction methods to accurately reflect the effects of construction disturbances. Dynamic adjustment of the time step achieved an optimal balance between computational efficiency and accuracy.

[0139] Ultimately, the Newton-Raphson iterative method was used to solve the nonlinear equations, setting a convergence criterion based on residual force or displacement thresholds. This was combined with MIDAS GTS software to achieve an efficient multi-field coupled solution. The calculation results were analyzed using monitoring point curves and cloud maps to accurately assess the impact of construction on the displacement, settlement, and stability of the existing station.

[0140] The specific implementation process is as follows:

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

[0142] The implementation of this process includes: opening the MIDAS GTS software, entering the geometric modeling module, accurately drawing the geometric shape of the structure and stratum according to the engineering drawings, and entering the size, position and other information of each part in detail. Then, in the material property setting window, according to the material test report, accurately set the elastic modulus, Poisson's ratio, density and other parameters for different structures and stratum materials. Then, switch to the boundary condition setting module, reasonably set the fixed boundary and free boundary, simulate the actual boundary constraint conditions, and add external loads, including ground stress, friction load between the subway station and the stratum, and additional loads caused by construction disturbances. Finally, use the meshing function, select the adaptive meshing method, and customize the input derived stress gradient tensor calculation formula The data is then brought into the calculation, the grid density is automatically adjusted, key areas such as the dark-bored tunnel and the areas adjacent to existing subway stations are refined, and the construction of the finite element three-dimensional basic calculation model is completed.

[0143] In an exemplary embodiment, more specific implementation contents include:

[0144] When establishing the finite element foundation model in MIDAS GTS software, the settings for the sand layer are as follows:

[0145] In the material constitutive model selection interface, select the Mohr-Coulomb model. Then, according to the detailed geological survey report, obtain the cohesion of the sand layer. and internal friction angle Accurately input the above parameters in the model parameter input column, and customize the input to derive the mechanical constitutive model formula of the sand layer. In subsequent calculations, the mechanical response of the sand layer under different stress states is accurately simulated, including calculations of stress, strain, and deformation. This more realistically reflects the changes in the mechanical properties of the sand layer during underground excavation construction, ensuring the accuracy of the overall model.

[0146] In the boundary condition setting module of MIDAS GTS software, the boundary conditions of the finite element foundation model are carefully set. Specifically, for fixed boundaries, the appropriate constraint type is selected to constrain the displacement freedom of the model boundary in specific directions. This simulates the constraining effect of bedrock on the structure in real projects, limiting the displacement of the structure in certain directions. For example, vertical displacement is constrained at the bottom boundary to simulate the support of the stratum on the structure. For free boundaries, the settings are ensured to be consistent with the actual situation, allowing the structure to deform freely according to the actual stress and deformation conditions at this boundary. In the load addition function, various load factors are fully considered. When adding external loads, the load magnitude, direction, and application location are accurately entered based on the actual load analysis of the project. For in-situ stress, calculation and input are based on geomechanical principles and on-site in-situ stress test data. Friction loads caused by subway stations and the stratum are considered and appropriately calculated and entered based on the contact conditions between the station structure and the stratum and the range of the relevant friction coefficient. Additional loads caused by construction disturbances are estimated and added based on the construction process and on-site monitoring data. Through these operations, it is ensured that the stress state of the model truly reflects the actual engineering situation and the reliability of the model calculation results is improved.

[0147] When meshing, select the adaptive meshing option in the meshing function. In its parameter setting area, enter the derived stress gradient tensor calculation formula The software automatically calculates stress gradients across the entire model, identifying key areas with significant stress variations, such as the vicinity of tunnels and existing subway stations. For these critical areas, the software automatically refines the mesh according to pre-set rules, increasing the number of elements and reducing the mesh size. In areas with relatively gentle stress variations, the software appropriately increases the mesh size and reduces the number of elements. This approach effectively controls computational effort and improves efficiency while ensuring accuracy.

[0148] 2. Multi-physics coupling model considering the full coupling effects of seepage, deformation and temperature:

[0149] This process involves creating a formation seepage model based on porous media theory within the seepage analysis module of MIDAS GTS. Based on on-site geological survey and test data, parameters such as formation permeability are accurately input into the model parameter settings. The software's built-in Biot consolidation theory is used to describe the relationship between soil deformation and seepage. The construction phase analysis function considers the impact of formation deformation on seepage paths and permeability for each construction stage, achieving accurate simulation of the coupled process of groundwater flow and formation deformation at each construction stage.

[0150] In an exemplary embodiment, more specific implementation contents include:

[0151] Enter the seepage analysis module in the MIDAS GTS software and choose to build a seepage model based on porous media theory. During the model construction process, based on the on-site geological survey data, including information such as the lithology and pore structure of the stratum, as well as the permeability coefficient data obtained from pumping tests and water pressure tests, the formation permeability and other related parameters are accurately input in the formation permeability parameter setting interface of the software. The accurate setting of these parameters is the key to the model's ability to accurately reflect the formation seepage characteristics, and provides a reliable data basis for subsequent consideration of fluid-solid coupling effects and analysis of the impact of groundwater on the project. For example, for strata with different lithologies, the corresponding permeability parameters are accurately set based on the differences in permeability coefficients determined by the experiment, so that the seepage model is more in line with the actual formation conditions.

[0152] In the seepage model setting of MIDAS GTS software, the steady-state seepage equation coupled with the anisotropic Darcy law and the continuity equation derived by custom input is used. The finite volume method is used to discretize the seepage equation. In the parameter setting of the discrete process, the discrete form of the control unit is customized. , accurately set parameters such as the surface area calculation method (such as selecting an appropriate area calculation formula based on the cell geometry), the distance measurement method (clarifying the measurement rules from the surface to the cell center), and the calculation and assignment of the equivalent permeability tensor. By correctly setting these parameters, it is possible to accurately solve the seepage equation and obtain relevant seepage results such as the hydraulic head distribution in the formation, providing data support for subsequent analysis of groundwater flow patterns and fluid-solid interaction.

[0153] In the multi-physics coupling setting module of MIDAS GTS software, the seepage equation and the solid deformation control equation are coupled according to the mixture theory. In the coupling parameter setting interface, according to the physical and mechanical properties of the rock and soil in the actual project, the control equation of the fluid-solid coupling system derived by self-defined input is , The additional strain rate term in the seepage equation reflects the bidirectional coupling effect between fluid seepage and solid deformation. By accurately setting these parameters, the interaction between the two during the fluid-solid coupling process is simulated, and the mechanical relationship between groundwater and strata and structures in underground engineering is more realistically reflected.

[0154] In the seepage model parameter adjustment function of MIDAS GTS software, a custom formula is created based on the occurrence parameters (dip, inclination, density) of the faults and joints in the formation. Correct the permeability tensor. By obtaining parameters and using formulas, the corrected permeability tensor is automatically calculated and applied to the fluid-solid coupling equations. This accurately characterizes the guiding effect of geological structures on the seepage path, making the model more consistent with the seepage conditions under actual geological conditions. For example, in areas with faults, correcting the permeability tensor can more accurately simulate the changes in groundwater seepage near the fault and its impact on surrounding strata and structures.

[0155] In the multi-physics coupling extension function of MIDAS GTS software, the correction relationship between the temperature field and the permeability derived by custom input is In the temperature field and seepage field coupling setting interface, input the rock thermal expansion coefficient determined by thermodynamic experiments. , fluid viscosity at different temperatures During the calculation process, the permeability is dynamically adjusted in real time based on this correction relationship, fully accounting for the impact of temperature changes on seepage characteristics, making the seepage calculation results more accurate. For example, when performing underground engineering calculations in geothermal areas, considering the impact of temperature on permeability can more accurately analyze groundwater flow.

[0156] In the advanced multi-physics coupling module of MIDAS GTS software, the temperature field and fluid-solid coupling system are coupled through the energy conservation equation. In the control equation setting interface, the control equation of the fully coupled seepage-deformation-temperature coupling derived by custom input is used. Achieve accurate simulation of full coupling of seepage, deformation and temperature, and fully consider the interaction between multiple physical fields. During the setting process, accurately input the equivalent heat capacity of rock and fluid , equivalent thermal conductivity , fluid convection heat transfer , heat source term converted from mechanical work of solid deformation The method can simulate the interaction among temperature field, seepage field and deformation field by adjusting parameters such as temperature, seepage and deformation, and provide a more comprehensive method for underground engineering analysis under complex geological conditions.

[0157] After the MIDAS GTS software completes the seepage-deformation-temperature full coupling simulation, use the software's post-processing function to analyze the results. View the variable cloud maps of the temperature field, seepage field, and deformation field to intuitively grasp the distribution of each field, such as the temperature cloud map to see the temperature distribution, and the seepage field cloud map to determine the seepage direction. Set monitoring points at key locations to obtain the time-varying curves of physical quantities such as temperature, pore water pressure, and displacement. When analyzing the impact of temperature on the seepage field, customize the formula derived by inputting By comparing the seepage field data with temperature changes, we can see the seepage changes caused by changes in permeability. We can also study the effect of pore pressure in the seepage field on the deformation field. By using the fluid-solid coupling equation, we can analyze the stress, strain, and displacement changes in the deformation field when the pore water pressure changes.

[0158] 3. Accurately calculate the rigidity of underground vertical pile foundation:

[0159] The implementation of this process includes: using the formula editor or custom calculation function in MIDAS GTS software, custom inputting the derived pile foundation force and displacement formulas calculated by theoretical load and elastic foundation model , obtain the soil cover weight from the engineering survey report and structural design documents , soil cover thickness , pile cross-sectional area , structural deadweight , live load , foundation soil reaction coefficient , pile length , pile bending stiffness EI and other related parameters and input to calculate the initial stiffness of the pile foundation. Considering the influencing factors such as soil squeezing effect and negative friction resistance, the multi-factor correction formula is used in the parameter correction function of the model. , determine the pile material hardening model according to the pile construction technology, the properties of the soil around the pile, etc. , pile-soil contact stiffness The initial stiffness is corrected by using the correction parameters and the corrected stiffness is applied to the pile foundation stiffness parameter position in the foundation calculation model.

[0160] In an exemplary embodiment, more specific implementation contents include:

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

[0162] In the stiffness calculation and correction function module of MIDAS GTS software, the multi-factor correction formula derived by custom input is Calculate the corrected pile foundation stiffness. First, obtain the initial stiffness calculated previously. Then, obtain the pile material hardening model from the pile material performance test report The pile-soil contact stiffness is obtained from the pile-soil interaction research data and field test data. Input these parameters into the correction parameter setting area of the software, and the software will automatically calculate according to the formula to obtain the corrected pile foundation stiffness, which improves the accuracy of the pile foundation stiffness calculation and makes it more consistent with the mechanical characteristics of the pile foundation in actual engineering.

[0163] 4.Simulate the construction process:

[0164] The implementation of this process includes: in the construction phase analysis module of MIDAS GTS, the excavation is divided into multiple stages according to the detailed construction organization design plan. In the setting of each stage, the corresponding excavation and support steps are clearly defined, and the soil excavation and support structure construction process is simulated by activating or disabling the corresponding units. When activating or disabling units, the activation time, stiffness change and other parameters of the units are reasonably set according to the construction sequence and process requirements to truly reflect the changes in the mechanical state of the soil and structure during the construction process. The incremental method is used to calculate the internal forces, deformations and stratum displacements of the structure. In the calculation method settings, the derived stress increment formula is customized by inputting , set the elastic strain energy calculation method (such as selecting a suitable elastic constitutive model to determine the elastic stiffness matrix ), strain increment solution method and other parameters, the software follows the incremental method principle to gradually calculate the increments of stress, strain and stratum displacement at each construction stage. At the same time, considering the timeliness of the support structure, in the material time-varying characteristics setting, for the support structure, the derived elastic modulus over time formula is customized. , obtain the initial elastic modulus from the material performance research report and engineering experience data of the supporting structure and attenuation coefficient Parameters such as the load and load are entered into the software's material time-varying parameter settings column. The software dynamically updates the elastic modulus of the support structure during the calculation process. Furthermore, considering the impact of different excavation methods on ground disturbance, in the construction simulation settings, different excavation methods (such as the step method, CD method, and CRD method) are simulated by applying corresponding equivalent loads in the model based on their mechanical characteristics and construction steps. In the equivalent load setting interface, based on engineering experience and theoretical analysis, the equivalent load size, direction, and application location corresponding to different excavation methods are determined and entered into the software.

[0165] In an exemplary embodiment, more specific implementation contents include:

[0166] In the construction phase analysis module of the MIDAS GTS software, excavation is divided into multiple stages according to the construction organization design plan. 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, and then construct the corresponding support structure. During the simulation process, the soil excavation and support structure construction process are simulated by activating or disabling the corresponding units. When activating the units, the activation time of the units is reasonably set according to the actual construction sequence and process requirements to ensure the accuracy of the simulated construction sequence; for the support structure units, their stiffness change parameters must also be set to simulate the changes in the mechanical properties of the support structure during the construction process. Through these settings, the changes in the mechanical state of the soil and structure over time during the construction process are truly reflected, providing accurate simulation data for analyzing the impact of construction on existing subway stations.

[0167] In the calculation method setting of MIDAS GTS software, select the incremental method to calculate structural stress, strain and formation displacement. In the incremental method calculation parameter setting interface, enter the derived stress increment formula by custom input Parameter settings are performed. First, determine the elastic strain energy calculation method and select an appropriate model based on the actual engineering material properties. Next, set the strain increment solution method to ensure the accuracy and stability of the calculation. Following the incremental method, incremental stress, strain, and ground displacement are calculated at each construction stage. By accumulating these incremental values, the stress, strain, and ground displacement results for each construction stage are obtained. When selecting the elastic strain energy calculation model, consider the material's stress-strain curve and other characteristics to ensure that the calculation results are consistent with the material's actual mechanical behavior.

[0168] In the calculation control parameter setting of MIDAS GTS software, the formula derived by custom input is Dynamic adjustment of time step. Characteristic length can be obtained from engineering design data , get the elastic modulus from the material properties report and density Parameters such as and are entered. The time step is automatically calculated and dynamically adjusted based on this formula. During the calculation process, when the mechanical response of the structure or stratum changes significantly, the time step is automatically reduced to improve calculation accuracy. When the mechanical response changes slightly, the time step is appropriately increased to improve calculation efficiency, ensuring a balance between the reliability of the calculation results and the efficiency of the calculation. For example, in the early stages of tunnel excavation, when the stratum stress changes dramatically, the software automatically reduces the time step to accurately capture the mechanical response. As construction progresses, the stratum gradually stabilizes, and the time step is appropriately increased to speed up the calculation.

[0169] In the material time-varying property setting of MIDAS GTS software, the change of mechanical properties of the support structure over time is considered. In the material parameter setting interface of the support structure, the formula of the elastic modulus of the support structure over time is customized and input. Get the initial elastic modulus from the material properties research report of the supporting structure and similar engineering experience data and attenuation coefficient Parameters such as α and β are entered into the software's Time-Varying Material Parameters section. During the calculation process, the software dynamically updates the elastic modulus of the support structure based on this formula in real time, accurately simulating the evolution of the support structure's mechanical properties during construction due to factors such as material aging and aging. For example, for steel supports, the attenuation coefficient is determined based on their material properties and previous engineering data to simulate the decline in elastic modulus during long-term construction, more realistically reflecting the actual mechanical state of the support structure.

[0170] The construction simulation settings in MIDAS GTS software simulate the effects of different excavation methods (such as the bench method, CD method, and CRD method). When simulating different excavation methods, equivalent loads are applied to the model based on their mechanical characteristics and construction steps. Taking the bench method as an example, the impact on the stratum and structure is analyzed based on the excavation sequence and soil unloading characteristics of the bench method, and the magnitude, direction, and application location of the equivalent load are determined. These parameters are entered into the equivalent load setting interface, and the software applies the equivalent load to simulate the mechanical effects of the bench method on the stratum and structure during construction. Similarly, for the CD and CRD methods, equivalent loads are determined and applied using similar methods to simulate the effects of different excavation methods on the stratum and structure, providing a basis for comparing and optimizing engineering options. For example, by comparing the ground displacement and structural stresses generated by the bench method and the CD method under the same geological conditions and engineering requirements, this can assist in selecting the more appropriate construction method.

[0171] 5. Solve through finite element iteration:

[0172] The implementation process involved iterative finite element analysis within MIDAS GTS software. Within the solution settings, convergence criteria based on residual forces or displacements were set for the nonlinear equations arising from material nonlinearities and fluid-structure interaction. During each construction phase, the software iteratively updated the solution, adapting to changes in the mesh configuration and time-dependent material properties to ensure convergence of the model calculations. This ensured accurate structural responses were obtained to assess the impact of the underpass on the existing subway station.

[0173] In an exemplary embodiment, more specific implementation contents include:

[0174] In MIDAS GTS software, an iterative method such as the Newton-Raphson method is selected for finite element iterative solution. In the solution setting dialog box, for the nonlinear equations caused by material nonlinearity and fluid-structure interaction, a convergence criterion based on residual force or displacement is set. For example, a component of the residual force or a component of the displacement is set to be less than a specific threshold (such as ) is considered converged. During each construction phase, the software continuously updates the solution according to the selected iteration method to adapt to changes in the mesh configuration (such as mesh deformation caused by soil excavation and support structure construction during construction) and time-dependent material properties (such as the change in the elastic modulus of the support structure over time). This continuous iteration ensures convergence of the model calculation, thereby obtaining accurate structural response and ground displacement results.

[0175] Based on the above examples, the present invention closely integrates the actual engineering situation during modeling and analysis, fully considering the coupling of multiple physical factors and the dynamic changes of the construction process. Its core advantages are reflected in the following three aspects:

[0176] First, through the fluid-solid coupling model and the seepage-deformation-temperature full coupling mechanism, the limitations of traditional methods in simulating groundwater action, space-time effects and multi-physical field interactions are broken through.

[0177] Secondly, the use of adaptive meshing and incremental dynamic simulation can significantly reduce manual modeling errors and achieve efficient simulation of complex construction processes.

[0178] Third, the model can be quickly adapted to its needs by making moderate modifications to the corresponding parameters and construction phase simulations, significantly enhancing its flexibility and scope of application.

[0179] Therefore, the present invention effectively solves the problems of complex multi-physical field coupling, difficult construction process simulation, and difficulty in balancing calculation accuracy and efficiency in the analysis of the impact of underground excavation on existing subway stations, 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 merely preferred implementations and are not intended to limit the present invention. It should be noted that those skilled in the art will be able to make modifications, equivalent substitutions, and improvements without departing from the spirit and scope of the present invention and the claims, all of which should be included within the scope of protection 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 3D finite element 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 coupling model considering the full coupling effects of seepage, deformation, and temperature is constructed; S3. Calculate the vertical pile foundation stiffness of the underground excavation, and modify it based on the soil squeezing effect and negative friction. Apply the modified vertical pile foundation stiffness to the finite element three-dimensional foundation calculation model. S4. Divide the underground excavation construction into multiple stages, simulating the process of ground unloading, support structure construction, and water-soil-fluid-solid coupling during precipitation. Use the incremental method to calculate structural stress, deformation, and ground displacement, and analyze the timeliness of the support structure and the impact of different excavation methods on ground disturbance. S5. Obtain structural responses through iterative finite element analysis and assess the impact of underground tunneling on existing subway stations. In step S2, a multi-physics coupling model considering the full coupling effects 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 effects of seepage, deformation, and temperature. The governing equation of the seepage model is the steady-state seepage equation coupled with the anisotropic Darcy law and the continuity equation: ； in, is the permeability tensor, is the water head value; 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. Its control equation is: ； in, is the equivalent heat capacity of rock and fluid; is the equivalent heat transfer coefficient; is the fluid convection heat transfer term; is the heat source term converted from mechanical work of solid deformation; T represents temperature; 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 Permeability increment of the fault strip; 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, Temperature The permeability under is the initial permeability, Temperature The fluid viscosity under is the fluid viscosity at the reference temperature, is the thermal expansion coefficient of rock, calibrated through thermodynamic experiments.

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

3. The method for analyzing the impact of underground excavation on existing subway stations according to claim 1, characterized in that: In step S1, the constructed finite element three-dimensional foundation calculation model includes layered modeling of strata, and different strata use 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 an existing subway station according to claim 1, characterized in that: In step S3, the method for calculating the stiffness of the concealed excavation vertical pile foundation is: Calculation of pile foundation forces using theoretical loads and elastic foundation models and displacement : ； in, It is heavy soil covering; is the thickness of the cover soil; is the cross-sectional area of the pile; The weight of the structure; is the live load; is the foundation soil reaction coefficient; is the pile length; is the pile bending stiffness; Based on pile foundation force and displacement , calculate the initial stiffness of the concealed vertical pile foundation.

5. The method for analyzing the impact of underground excavation on an existing subway station as claimed in claim 4, characterized in that: In step S3, the stiffness of the underground vertical pile foundation 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.

6. The method for analyzing the impact of underground excavation on an existing subway station 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.

7. The method for analyzing the impact of underground excavation on an existing subway station as claimed in claim 6, characterized in that: In step S4, the time step is dynamically adjusted during the simulation of ground unloading, support structure construction, and precipitation water-soil fluid-solid coupling. , and satisfy: ； in, is a constant, is the characteristic length, is the elastic modulus, is the density.

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