Method for analyzing deformation of subway tunnel by foundation pit construction in saturated soft clay area

Abstract

The invention relates to the field of supply and demand interaction of a power system, and discloses a method for analyzing deformation of a subway tunnel by foundation pit construction in a saturated soft clay area, which comprises the following steps of: a, acquiring geological information of an area to be analyzed; b, establishing a three-dimensional numerical model based on the geological information, and setting a soil constitutive relation and boundary conditions; c, simulating and calculating a displacement field and a stress field through the three-dimensional numerical model; and step d, according to the displacement field and the stress field, analyzing and determining a deformation control measure for the existing subway tunnel. According to the method, a three-dimensional numerical model containing soil layering, a tunnel structure and a supporting system is established through geological information, deviation caused by excessive simplification of the model in a traditional analysis method is avoided, the model is calibrated through field monitoring data, the displacement field and the stress field obtained through calculation can more accurately reflect engineering practice, and the engineering practice is more accurate. And the accuracy of predicting the deformation of the existing subway tunnel is obviously improved.

Description

Technical Field

[0001] This invention relates to the field of power system supply and demand interaction technology, and in particular to an analysis method for the deformation of subway tunnels caused by foundation pit construction in saturated soft clay areas. Background Technology

[0002] With the rapid development of urban underground space, the number of foundation pit projects around subway tunnels is increasing. In saturated soft clay areas, due to the soil's low strength, high compressibility, and poor permeability, foundation pit excavation easily causes deformation of the surrounding soil, leading to displacement, settlement, and even cracking of adjacent subway tunnel structures. Currently, scholars both domestically and internationally have conducted extensive research on the interaction between foundation pits and tunnels, mainly using methods such as field monitoring, theoretical analysis, and numerical simulation to assess tunnel deformation. However, the nonlinearity, rheology, and anisotropy of saturated soft clay pose significant challenges to deformation prediction and control. Existing technologies mostly focus on single-factor analysis, lacking systematic research on the coupled effects of multiple factors such as geological conditions, support methods, and construction techniques.

[0003] Specific solutions in existing technologies: In existing technologies, the following methods are usually used to control tunnel deformation caused by foundation pit construction: (1) Optimization of support structure, such as using rigid support such as diaphragm walls and cast-in-place piles; (2) Soil reinforcement, such as grouting reinforcement and mixing pile reinforcement to improve soil strength and stiffness; (3) Optimization of construction technology, such as zonal and layered excavation and control of excavation rate to reduce construction disturbance. Diaphragm walls have the advantages of high stiffness and small deformation, but they are expensive and have a long construction period; cast-in-place piles have lower costs, but their deformation control effect is limited. Grouting reinforcement can effectively improve soil properties, but there is a problem of uneven grout diffusion; mixing pile reinforcement has good uniformity, but its depth is limited. Although construction technology optimization can reduce instantaneous deformation, it is insufficient for controlling long-term creep deformation.

[0004] However, the existing technology still has the following shortcomings: (1) The selection of support structure and soil reinforcement lacks specificity and is difficult to adapt to the complex geological characteristics of saturated soft clay; (2) The optimization of construction technology relies heavily on experience and lacks quantitative guidance; (3) The existing analysis methods do not fully consider the multi-field coupling effect of soil-structure-construction, resulting in insufficient deformation prediction accuracy; (4) The control measures have poor operability and are difficult to implement effectively in actual engineering. Summary of the Invention

[0005] The purpose of this invention is to provide an analysis method for the deformation of subway tunnels caused by foundation pit construction in saturated soft clay areas. This method solves the problems in the prior art where the analysis method fails to fully consider the coupling effect of multiple factors, resulting in insufficient accuracy in deformation prediction, and the control measures formulated based on it lack pertinence, quantitative guidance, and operability.

[0006] To achieve the above objectives, the first aspect of this invention provides a method for analyzing the deformation of subway tunnels caused by foundation pit construction in saturated soft clay areas. This method includes the following steps: Step a) Obtain geological information for the area to be analyzed. This geological information includes: geological survey data, design parameters of existing subway tunnels, design parameters of the foundation pit to be constructed, and foundation pit construction data. The geological survey data contains the soil physical and mechanical parameters required for subsequent calculations, such as the density γ of each soil layer. i Effective cohesion c ′ Effective internal friction angle φ ′ Compression index C c Initial void ratio e0, consolidation coefficient c v And the coefficient of earth pressure at rest, K0.

[0007] Step b: Based on the geological information, establish a three-dimensional numerical model that includes soil stratification, the existing subway tunnel structure, and the support system of the foundation pit, and set soil constitutive relations and boundary conditions for the three-dimensional numerical model.

[0008] Step c: Simulate the step-by-step excavation process of the foundation pit using the three-dimensional numerical model, and calculate the displacement field and stress field of the existing subway tunnel during the foundation pit excavation process.

[0009] Step d: Based on the displacement field and stress field, analyze and determine deformation control measures for the existing subway tunnel.

[0010] Through the above steps, this invention provides a systematic analysis process. By establishing an accurate numerical model and simulating the construction process, it can quantitatively calculate the impact of foundation pit excavation on existing subway tunnels, providing data support for formulating scientific control measures, thereby improving the accuracy of deformation prediction and the effectiveness of control measures.

[0011] In a specific embodiment, step b, the step of setting boundary conditions for the three-dimensional numerical model, includes: calculating the initial geostress field containing the existing subway tunnel as the initial boundary conditions. This calculation process includes: First, the effective stress of the soil is determined based on the effective stress principle, and the formula is as follows: σ ′ =σ-u; In the formula, σ ′ σ is the effective stress, σ is the total stress, and u is the pore water pressure.

[0012] Secondly, calculate the total vertical stress σ at any depth. v : In the formula, σ vγ represents the total vertical stress at depth z; n represents the total number of soil layers above the calculation point; i h is the density of the i-th soil layer by weight; i Let be the thickness of the i-th soil layer.

[0013] Finally, the initial horizontal effective stress σ is calculated based on the at-rest earth pressure coefficient K0. ′ h0 : σ ′ h0 =K0·σ ′ v ; In the formula, σ ′ v This represents the effective vertical stress at the corresponding depth.

[0014] Preferably, in step b, the soil constitutive relation is the Mohr-Coulomb criterion, used to simulate the nonlinear behavior of saturated soft clay, and its expression is: τ f =c ′ +σ ′ n tan(φ ′ ); In the formula, τ f c is the shear strength on the shear plane; ′ The effective cohesion of the soil; σ ′ n φ is the normal effective stress on the shear plane. ′ The effective internal friction angle of the soil.

[0015] Furthermore, the three-dimensional numerical model employs a contact algorithm to simulate the interaction between the saturated soft clay and the existing subway tunnel structure and the support system of the foundation pit.

[0016] In one embodiment, step c, simulating the step-by-step excavation process of the foundation pit, employs an incremental method. This simulation process considers the stress field changes caused by excavation, including calculating the active earth pressure σ on the support structure. ′ ha : In the formula, σ ′ ha For active earth pressure on the support structure; K a σ is the active earth pressure coefficient; ′ v c represents the effective vertical stress at the corresponding depth. ′ It represents the effective cohesion of the soil.

[0017] Meanwhile, the simulation also takes into account the change in additional soil stress Δσ caused by excavation unloading. ′ v : Δσ ′ v =-q·I; In the formula, q is the total unloading stress corresponding to the excavation depth of the foundation pit, and I is the stress influence coefficient.

[0018] Furthermore, in step c, regarding the time effect of deformation of saturated soft clay, its excess pore water pressure u e The dissipation process follows a one-dimensional consolidation differential equation: In the formula, u e t is the excess pore water pressure; t is time; z is the coordinate along the consolidation direction; c v The soil consolidation coefficient; The rate of change of excess pore water pressure with respect to the coordinate along the consolidation direction; Therefore, the final consolidation settlement S of the soil layer can be calculated. c : In the formula, H is the thickness of the compressive soil layer, and σ ′ v0 S represents the initial vertical effective stress at the midpoint of the soil layer. c C represents the final consolidation settlement. c σ is the compression index; e0 is the initial void ratio of the soil layer; Δσ ′ v This represents the vertical effective stress increment at the midpoint of the soil layer caused by changes in external loads. Simultaneously, the lateral subsidence distribution of the land surface, i.e., the subsidence trough S(x), can be predicted: In the formula, S max The maximum surface subsidence is given by x, which is the horizontal distance from the subsidence centerline, and i is the subsidence trough width coefficient.

[0019] In a specific embodiment, step d, the step of analyzing and determining deformation control measures, includes assessing the impact of soil deformation on the tunnel structure, specifically by calculating the bending moment M(θ) of the tunnel lining: In the formula, R is the equivalent radius of the tunnel, p(α) is the non-uniform radial pressure distribution function acting on the tunnel lining, and K M (θ, α) is the bending moment influence function; θ and α are angle variables.

[0020] In a preferred embodiment, prior to step d, the method further includes: acquiring on-site monitoring data of the existing subway tunnel; comparing the displacement field and stress field calculated in step c with the on-site monitoring data; and calibrating the three-dimensional numerical model based on the comparison results.

[0021] Furthermore, the step of analyzing and determining targeted deformation control measures includes: performing sensitivity analysis based on the calibrated three-dimensional numerical model to determine the parameter combination that significantly affects the deformation of the existing subway tunnel, and using this parameter combination as the basis for determining the deformation control measures.

[0022] Specifically, the parameter combination includes at least one of the support forms and reinforcement methods applied to the foundation pit; or, the parameter combination also includes optimization of the construction process for the foundation pit.

[0023] In a specific embodiment, the deformation control measures determined in step d include: using prestressed anchor cables for combined support in the foundation pit, or setting isolation piles between the foundation pit and the existing subway tunnel.

[0024] A second aspect of the present invention provides an analysis system for the deformation of subway tunnels caused by foundation pit construction in saturated soft clay areas. This system is used to implement the method described in any of the preceding claims, comprising: The data collection module is used to acquire geological information about the area to be analyzed. The model building module, connected to the data collection module, is used to build a three-dimensional numerical model and set the soil constitutive relationship and boundary conditions based on the geological information. The analysis module, connected to the model building module, is used to simulate the step-by-step excavation process of the foundation pit through the three-dimensional numerical model, and to calculate the displacement field and stress field of the existing subway tunnel during the foundation pit excavation process. The control measures module, connected to the analysis module, is used to analyze and determine deformation control measures for the existing subway tunnel based on the displacement field and stress field calculated by the analysis module.

[0025] In summary, the present invention has at least one of the following beneficial technical effects: 1. This invention establishes a three-dimensional numerical model that includes soil stratification, tunnel structure, and support system based on geological information. This eliminates the bias caused by the oversimplification of the model in traditional analysis methods. Furthermore, by calibrating the model with field monitoring data, the calculated displacement and stress fields can more accurately reflect the actual engineering situation, significantly improving the accuracy of deformation prediction for existing subway tunnels.

[0026] 2. This invention, based on a three-dimensional numerical model and sensitivity analysis method, can quantitatively assess the influence weight of different support forms, reinforcement methods or construction process parameters on tunnel deformation. Therefore, it can identify the most critical control factors, making the determined deformation control measures more targeted and effective, and avoiding the problems of poor economy or poor effect of control schemes caused by blind selection or reliance on experience in traditional methods.

[0027] 3. By simulating the entire construction process before the actual excavation of the foundation pit and calculating the deformation magnitude and distribution of the existing subway tunnel in advance, we can provide project decision-makers with intuitive and quantitative data, enabling risk assessment and control measures to shift from post-remedial measures to pre-control measures, thereby improving the safety and controllability of the project construction. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 This is a schematic diagram of the system architecture of the present invention. Detailed Implementation

[0029] Please see the appendix Figure 1 , attached Figure 1 This invention provides a flowchart illustrating a method for analyzing the deformation of subway tunnels during foundation pit construction in saturated soft clay areas. The method includes: Step a: Data acquisition begins. This step involves collecting geological information related to the project, including geological survey data, as well as design parameters related to the project entity, including design and construction data for existing subway tunnels and foundation pits to be built.

[0030] Next, we proceed to step b: the model building stage. This step transforms the engineering scenario into a digital model that can be used for mechanical analysis by a computer. The process includes building a three-dimensional numerical model that reflects the real geometric relationships of the soil layers, tunnel structure, and foundation pit support system, and setting constitutive relations for the soil that describe the mechanical behavior of the materials, as well as boundary conditions that represent the initial state of the project.

[0031] Next, step c: simulation calculation. This step uses the three-dimensional numerical model established in the previous step, with all parameters pre-set, to dynamically simulate the phased excavation process of the foundation pit. By calculating and outputting the specific impact of the foundation pit excavation on the adjacent existing subway tunnel, the results are expressed as the displacement field and stress field at various points on the tunnel structure.

[0032] Finally, in step d: the analysis and decision-making stage, the displacement and stress field data obtained in step c are analyzed. Based on the magnitude and distribution of tunnel deformation and stress, their impact on the safety of the tunnel structure is assessed. Based on this analysis, one or more targeted and operable deformation control measures are determined to ensure the safety of the existing subway tunnel.

[0033] In one specific embodiment: First, step a is performed to obtain geological information about the area to be analyzed. This geological information serves as the foundational data input for all subsequent model building and analytical calculations. The geological information is systematically collected and organized for use in subsequent steps.

[0034] Specifically, the acquisition of geological information includes, but is not limited to, the following: 1. Obtain geological survey data. This data is obtained by reviewing the geological survey report at the engineering site, which contains a series of soil physical and mechanical parameters used for subsequent calculations.

[0035] 2. These parameters include, but are not limited to: the density γ of each soil layer. i Effective cohesion c ′ Effective internal friction angle φ ′ Compression index C c Initial void ratio e0, consolidation coefficient c v And the coefficient of earth pressure at rest, K0. These parameters provide the necessary input values ​​for subsequent in-situ stress calculations, constitutive relation definitions, and consolidation settlement analysis.

[0036] Second, obtain the design parameters of existing subway tunnels. These parameters are obtained by consulting the design drawings and as-built data of existing subway tunnels. They mainly include: the geometric dimensions of the tunnel, such as the outer contour radius R of the tunnel lining; the material properties of the tunnel lining, such as the elastic modulus, Poisson's ratio, and unit weight; and the precise axial coordinates and burial depth of the tunnel in three-dimensional space.

[0037] Third, obtain the design parameters and construction data of the foundation pit to be constructed. These parameters are obtained by reviewing the support design scheme and construction organization design of the foundation pit. They mainly include: the plan dimensions and excavation depth of the foundation pit; the specific form and parameters of the foundation pit support system, such as the wall thickness, depth, and material parameters if a diaphragm wall is used, and the pile diameter, pile length, and pile spacing if cast-in-place piles are used; and the construction steps of the foundation pit, such as the thickness of each excavation layer, the order of excavation for each layer, and the predetermined excavation rate.

[0038] By performing step a, accurate data can be provided for the establishment of the three-dimensional numerical model in subsequent step b and the simulation calculation in step c.

[0039] Next, step b is executed, which is to establish a three-dimensional numerical model based on geological information, which is used to generate a digital model capable of mechanical analysis based on the input data.

[0040] Specifically, the first step in model building is creating a geometric model. Based on the soil layering data obtained in step a, and the spatial location and dimensional parameters of the existing subway tunnel and the foundation pit to be constructed, a solid model that accurately reflects the actual geometric relationships of the engineering site is established in a three-dimensional coordinate system. This geometric model includes three-dimensional solids of multiple soil layers, a three-dimensional solid of the subway tunnel lining structure, and a three-dimensional solid of the foundation pit support system (such as diaphragm walls or cast-in-place piles). The calculation range of the model should be sufficiently extended in both the horizontal and vertical directions to eliminate the interference of boundary effects on the calculation results.

[0041] Subsequently, after establishing the geometric model, material constitutive relations and contact conditions are set for each component in the model. For saturated soft clay, this embodiment uses the Mohr-Coulomb criterion as its soil constitutive relation to describe its nonlinear shear failure behavior under stress. The expression for this criterion is: τ f =c ′ +σ ′ n tan(φ ′ ); In the formula, τ f c is the shear strength on the shear plane; ′ The effective cohesion of the soil; σ ′ n φ is the normal effective stress on the shear plane. ′ The effective internal friction angle of the soil.

[0042] These parameters (c) ′ ,φ ′ The specific values ​​are derived from the geological survey data obtained in step a. For existing subway tunnel linings and foundation pit support structures, linear elastic constitutive relations are assigned.

[0043] Meanwhile, at the interfaces between the soil and the tunnel structure, and between the soil and the foundation pit support system, a contact algorithm is used to simulate the interaction between them, including the normal pressure transmission and the tangential friction behavior.

[0044] Finally, initial boundary conditions are set for the three-dimensional numerical model. The core of this process is to establish an initial geostress field that reflects the original state before excavation and to bring the model to equilibrium. This process is first based on the effective stress principle, the formula of which is: σ ′ =σ-u; In the formula, σ ′ σ is the effective stress, σ is the total stress, and u is the pore water pressure.

[0045] When calculating the initial geostress field, first calculate the total vertical stress σ at any depth in the soil. v The calculation formula is: In the formula, σ v γ represents the total vertical stress at depth z; n represents the total number of soil layers above the calculation point; i h is the density of the i-th soil layer by weight; i Let be the thickness of the i-th soil layer.

[0046] After obtaining the vertical stress, calculate the initial horizontal effective stress σ based on the at-rest earth pressure coefficient K0 obtained in step a. ′ h0 The calculation formula is as follows: σ ′ h0 =K0·σ ′ v ; In the formula, σ ′ v This represents the effective vertical stress at the corresponding depth.

[0047] The calculated initial geostress field is applied to the entire numerical model, and calculations are performed until the model reaches its initial equilibrium state.

[0048] After completing the above steps, a three-dimensional numerical model in equilibrium, containing accurate geometry, reasonable constitutive relations, and a true initial geostress field, is established. This model can then serve as the basis for subsequent step c, namely, the simulation calculation of the foundation pit excavation process, providing initial conditions.

[0049] After completing step b, the method proceeds to step c, namely, the simulation and analysis calculation of the excavation process. This step specifically involves using a three-dimensional numerical model in an initial equilibrium state to simulate the step-by-step excavation process of the foundation pit and calculating the displacement and stress fields generated by this process on the existing subway tunnel.

[0050] The simulation process employs an incremental method, discretizing the continuous foundation pit excavation process into a series of independent calculation steps. Each calculation step precisely corresponds to a specific working condition in the construction organization design, such as the excavation of a layer of soil, the erection or removal of a support, etc. The actual construction sequence is reproduced by successively activating or deactivating the elements in the model (for example, removing the element representing a certain layer of excavated soil from the calculation to simulate unloading).

[0051] Furthermore, during the simulated excavation and unloading process, the redistribution of the soil stress field is first calculated. This includes calculating the active earth pressure σ acting on the support structure after the foundation pit is excavated. ′ haThe calculation formula is as follows: In the formula, σ ′ ha For active earth pressure on the support structure; K a σ is the active earth pressure coefficient; ′ v c represents the effective vertical stress at the corresponding depth. ′ It represents the effective cohesion of the soil.

[0052] Simultaneously, the simulation must also consider the additional stress changes in the surrounding soil caused by excavation and unloading. The additional stress change Δσ in the soil due to excavation and unloading must be taken into account. ′ v The calculation formula is as follows: Δσ ′ v =-q·I; In the formula, q is the total unloading stress corresponding to the excavation depth of the foundation pit, and I is the stress influence coefficient.

[0053] For saturated soft clay regions, fluid-structure interaction calculations are also required to analyze the effects of deformation over time. This analysis considers the excess pore water pressure u. e The generation and dissipation of [something] follow a one-dimensional consolidation differential equation, expressed as follows: In the formula, u e t is the excess pore water pressure; t is time; z is the coordinate along the consolidation direction; c v The soil consolidation coefficient; The rate of change of excess pore water pressure with respect to the coordinate along the consolidation direction; Based on this, the final consolidation settlement S of the soil under additional stress can be calculated. c The calculation formula is as follows: In the formula, H is the thickness of the compressive soil layer, and σ ′ v0 S represents the initial vertical effective stress at the midpoint of the soil layer. c C represents the final consolidation settlement. c σ is the compression index; e0 is the initial void ratio of the soil layer; Δσ ′ v This represents the vertical effective stress increment at the midpoint of the soil layer caused by changes in external loads. In addition, the simulation can also output the predicted results of the lateral subsidence distribution of the land surface, namely the subsidence trough S(x), whose distribution law can be described by the following formula: In the formula, Smax The maximum surface subsidence is given by x, which is the horizontal distance from the subsidence centerline, and i is the subsidence trough width coefficient.

[0054] After completing the incremental calculations for all construction steps, a complete set of data will be output, which records in detail the displacement vectors (i.e., displacement fields) of each node on the subway tunnel structure and the stress tensors (i.e., stress fields) of each element in each step of the foundation pit excavation. This data will then be passed to the subsequent step d for analysis.

[0055] In a preferred embodiment, to improve the accuracy of numerical model predictions, a step of calibrating the three-dimensional numerical model is included before performing the final step d.

[0056] This step is performed after the foundation pit has been excavated to a predetermined depth and some on-site monitoring data has been obtained.

[0057] First, on-site monitoring data of existing subway tunnels is acquired. This data comes from monitoring instruments deployed at key locations in the tunnel structure, including but not limited to measured values ​​of vertical settlement, horizontal displacement, and lining strain at specific cross-sections. This data accurately reflects the actual deformation and stress state of the tunnel at the current stage of excavation.

[0058] Subsequently, the displacement and stress field results obtained in step c, which are from the same construction stage as the monitoring data, are compared with the acquired field monitoring data.

[0059] Specifically, the displacement calculation values ​​of nodes and the stress calculation values ​​of elements in the numerical model that correspond perfectly to the spatial locations of the field monitoring points are extracted and compared with the corresponding measured values ​​to determine the deviation between them.

[0060] If the deviation between the calculation results and the monitoring data exceeds the preset error range allowed by the project, the model calibration process will be initiated.

[0061] In one embodiment, the process is an iterative optimization process. Based on the magnitude and distribution characteristics of the deviation, parameter adjustment instructions are passed to the model. Subsequently, key input parameters in the model that exhibit uncertainty are adjusted. These parameters mainly refer to the physical and mechanical parameters in the soil constitutive relation set in step b, such as effective cohesion c. ′ Effective internal friction angle φ ′ Or soil deformation modulus.

[0062] After the model parameters are adjusted, the numerical model with updated parameters can be used to re-execute the simulation calculation process in step c to obtain a new set of displacement and stress field results.

[0063] At this point, the new calculation results are compared again with the field monitoring data. This iterative process (i.e., comparison to adjustment to recalculation) is repeated until the tunnel deformation and stress values ​​calculated by the model match the field monitoring values ​​to the preset accuracy requirements.

[0064] After completing this step, a three-dimensional numerical model calibrated with on-site monitoring data will be obtained. The parameters of the calibrated model will be closer to the actual geomechanical characteristics of the project, resulting in higher accuracy in predicting tunnel deformation during subsequent construction steps. This calibrated model will then be used to perform step d.

[0065] In a specific embodiment, after completing step c, or after completing the calibration of the model, the method performs step d, which involves receiving and analyzing the displacement field and stress field data of the existing subway tunnel, and determining targeted deformation control measures based on the analysis results.

[0066] Specifically, the calculation results are first evaluated by comparing the maximum displacement, uneven settlement, and stress values ​​of each key section of the tunnel with the deformation control standards or early warning thresholds required for the operation of the subway line.

[0067] To further quantify the specific impact of soil deformation on the internal forces of the tunnel structure, it is necessary to calculate the bending moment M(θ) of the tunnel lining under non-uniform pressure. The calculation formula is as follows: In the formula, R is the equivalent radius of the tunnel, p(α) is the non-uniform radial pressure distribution function acting on the tunnel lining, and K M (θ, α) is the bending moment influence function; θ and α are angle variables.

[0068] The calculated bending moment value is compared with the design bending bearing capacity of the tunnel structure to determine its safety.

[0069] In a preferred embodiment, if the initially calculated tunnel deformation or internal force exceeds the control standard, a sensitivity analysis based on a three-dimensional numerical model will be initiated.

[0070] This analysis was performed by setting multiple different calculation conditions in order to identify the combination of parameters that would have the most significant impact on tunnel deformation. Then, specific parameters were modified and the simulation was recalculated.

[0071] These calculation scenarios include, but are not limited to: changing the support method applied to the foundation pit, for example, changing the original cast-in-place pile support to diaphragm wall support for comparative calculation; or adding soil reinforcement methods, for example, adding grouting reinforcement or mixing pile reinforcement simulation to the model and analyzing their effect on suppressing tunnel deformation.

[0072] The parameter combination also includes the optimization of the foundation pit construction process. For example, setting different excavation sequences (such as segmented excavation, skip excavation) or adjusting the excavation rate, and calculating the final deformation of the existing subway tunnel under these different construction processes.

[0073] After completing the calculations for all preset working conditions, the calculation results for each working condition are normalized and compared to identify the most effective parameter combination for reducing tunnel displacement and stress. This parameter combination then serves as the core basis for determining the final deformation control measures.

[0074] Based on the results of the aforementioned sensitivity analysis, a set of clear and actionable deformation control measures is ultimately derived. For example, these measures could include: using prestressed anchor cables for combined support in the foundation pit to provide additional active support; or installing a row of isolation piles between the foundation pit and the existing subway tunnel to prevent deformation transmission. These determined control measures will then serve as the final construction optimization plan, guiding on-site construction.

[0075] Please see the appendix Figure 2 , attached Figure 2 This invention provides a schematic diagram of the system architecture for analyzing the deformation of subway tunnels during foundation pit construction in saturated soft clay areas. The system includes: The data collection module is used to acquire geological information of the area to be analyzed. The geological information includes: geological survey data, design parameters of existing subway tunnels, design parameters of the foundation pit to be built, and foundation pit construction data. In this embodiment, the data collection module is used to perform step a in the aforementioned method. This module is used to acquire and process all the basic data required for subsequent modeling and analysis. Specifically, this module acquires the physical and mechanical parameters of the soil from the geological survey report, the geometric dimensions, material properties, and spatial location information from the design drawings of existing subway tunnels, and the support parameters and phased construction conditions from the design scheme of the foundation pit to be constructed. In a preferred embodiment, this module is also used to acquire real-time tunnel deformation data measured by monitoring instruments deployed at the engineering site for model calibration.

[0076] The model building module is used to build a three-dimensional numerical model based on geological information, including soil stratification, existing subway tunnel structure, and foundation pit support system, and to set soil constitutive relations and boundary conditions for the three-dimensional numerical model. In this embodiment, the model building module is connected to the data collection module and is used to execute step b of the aforementioned method. This module receives data from the data collection module and builds a complete three-dimensional numerical model accordingly. Its specific functions include: constructing a geometric model that reflects the true spatial relationship between soil stratification, tunnel structure, and foundation pit support system; assigning material constitutive relations to different parts of the model, particularly specifying a Mohr-Coulomb constitutive model for saturated soft clay, and setting contact relationships between structures; and calculating and applying an initial geostress field that reflects the original state of the project, ensuring the model reaches equilibrium before calculation begins. During model calibration, this module is also responsible for adjusting specific soil parameters in the model according to instructions.

[0077] The analysis module is used to simulate the step-by-step excavation process of the foundation pit by using the three-dimensional numerical model established and set by the model building module, and to calculate the displacement field and stress field of the existing subway tunnel during the foundation pit excavation process. In this embodiment, the analysis module 30 is connected to the model building module 20, and its function is to execute step c in the aforementioned method. This module receives the numerical model that is already in equilibrium, output by the model building module, and solves and calculates it. Specific functions include: using an incremental method, simulating the excavation of the foundation pit soil and the application of the support structure step by step according to preset construction steps; during the simulation, calculating the soil stress redistribution, soil deformation, and consolidation settlement of saturated soft clay caused by excavation unloading; and finally calculating and outputting the displacement field and stress field of each point on the existing subway tunnel structure throughout the entire construction process.

[0078] The control measures module is used to analyze and determine deformation control measures for existing subway tunnels based on the displacement and stress fields calculated by the analysis module.

[0079] In this embodiment, the control measures module is connected to the analysis module, and its function is to execute step d in the aforementioned method. This module receives displacement and stress field data output by the analysis module and analyzes it to determine the final control scheme. Specifically, this includes: comparing the calculated tunnel deformation and stress values ​​with preset control standards; further evaluating the structural safety by calculating internal force indicators such as the tunnel lining bending moment; performing sensitivity analysis, i.e., simulating and calculating various different support forms, reinforcement methods, or construction techniques through the instruction analysis module, and comparing the results to identify the most effective parameter combination for controlling deformation; finally, based on the results of the sensitivity analysis, determining and outputting a set of clear and operable deformation control measures.

[0080] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for analyzing the deformation of a subway tunnel caused by the construction of a foundation pit in a saturated soft clay area, characterized in that, The method comprises the following steps: Step a, obtaining geological information of an area to be analyzed, the geological information comprising geological survey data, design parameters of an existing subway tunnel, design parameters of a foundation pit to be built, and construction data of the foundation pit; Step b, establishing a three-dimensional numerical model comprising soil layering, the structure of the existing subway tunnel, and a support system of the foundation pit based on the geological information, and setting soil constitutive relations and boundary conditions for the three-dimensional numerical model; Step c, simulating a step-by-step excavation process of the foundation pit through the three-dimensional numerical model, and calculating displacement fields and stress fields of the existing subway tunnel during the excavation process of the foundation pit; Step d, analyzing and determining deformation control measures for the existing subway tunnel according to the displacement fields and stress fields.

2. The method according to claim 1, wherein the method is characterized by, In step b, the soil constitutive relations are Mohr-Coulomb criteria for simulating nonlinear behavior of saturated soft clay; And the three-dimensional numerical model uses a contact algorithm to simulate the interaction between the saturated soft clay and the existing subway tunnel structure and the support system of the foundation pit.

3. The method according to claim 1, wherein the method is characterized by, In step c, the step of simulating the step-by-step excavation process of the foundation pit uses an incremental method to calculate displacement fields and stress fields of the existing subway tunnel at different excavation steps.

4. The method according to claim 1, wherein, Before the step of analyzing and determining the deformation control measures, it further comprises: Obtaining in-situ monitoring data of the existing subway tunnel; Comparing the calculated displacement fields and stress fields with the in-situ monitoring data, and calibrating the three-dimensional numerical model according to the comparison results.

5. The method according to claim 4, wherein the method is characterized by, The step of analyzing and determining the deformation control measures comprises: performing a sensitivity analysis based on the three-dimensional numerical model to determine a parameter combination that has a significant impact on the deformation of the existing subway tunnel, and using the parameter combination as a basis for determining the deformation control measures.

6. The method according to claim 5, wherein, The parameter combination comprises at least one of a support form and a reinforcement method applied to the foundation pit; wherein the support form is a diaphragm wall or a cast-in-place pile; and the reinforcement method is grouting reinforcement or mixing pile reinforcement.

7. The method according to claim 5, wherein the method is characterized by, The parameter combination further comprises construction process optimization for the foundation pit; wherein the construction process optimization comprises adjusting the excavation sequence or excavation rate of the foundation pit.

8. The method of claim 1, wherein the saturated soft clay area foundation construction is a subway tunnel deformation analysis method. In step d, the deformation control measures comprise using prestressed anchor cables for combined support in the foundation pit, or setting isolation piles between the foundation pit and the existing subway tunnel.

9. The method of claim 1, wherein the saturated soft clay area foundation construction is a subway tunnel deformation analysis method. The step of setting boundary conditions for the three-dimensional numerical model comprises: Calculating an initial geostress field comprising the existing subway tunnel as an initial boundary condition, wherein the calculation of the initial geostress field is based on the effective stress principle and the static earth pressure coefficient.

10. A system for analyzing the deformation of a subway tunnel caused by the construction of a foundation pit in a saturated soft clay area, for implementing the method for analyzing the deformation of a subway tunnel caused by the construction of a foundation pit in a saturated soft clay area according to any one of claims 1 to 9, characterized in that, It comprises: A data collection module for obtaining geological information of an area to be analyzed, the geological information comprising geological survey data, design parameters of an existing subway tunnel, design parameters of a foundation pit to be built, and construction data of the foundation pit; A model establishment module for establishing a three-dimensional numerical model comprising soil layering, the structure of the existing subway tunnel, and a support system of the foundation pit based on the geological information, and setting soil constitutive relations and boundary conditions for the three-dimensional numerical model; An analysis module is configured to simulate a step-by-step excavation process of the foundation pit by using the three-dimensional numerical model established and set by the model establishment module, and to obtain a displacement field and a stress field of the existing subway tunnel during the excavation process of the foundation pit; A control measure module is configured to analyze and determine a deformation control measure for the existing subway tunnel according to the displacement field and the stress field obtained by the analysis module.

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