Water-rich stratum foundation pit engineering SMW fender post support parameter optimization method and system

Abstract

The invention relates to the technical field of geotechnical engineering support, and provides a water-rich stratum foundation pit engineering SMW fender post support parameter optimization method and system, and the method comprises the steps: S1, obtaining an excavation calculation model; s2, physical and mechanical parameters of a water-rich stratum soil body to be excavated are determined; s3, parameters of an SMW fender post supporting structure are determined; s4, excavation calculation simulation; s5, calculating the upheaval value of the bottom of the foundation pit and the supporting lateral deformation of the SMW fender posts; s6, establishing a database; s7, quantitatively analyzing the contribution weight of each factor to the displacement of the foundation pit; and S8, determining an optimal supporting scheme. The system comprises a soil physical and mechanical parameter input module, an SMW fender post supporting structure parameter determination module, an excavation calculation simulation module, a foundation pit bottom upheaval and lateral deformation database, a weight determination module and a parameter optimization module. Compared with a traditional method, the optimal support parameter solution of the SMW fender post of the water-rich stratum foundation pit engineering can be more accurately given.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering support technology, and in particular to a method and system for optimizing the support parameters of SMW retaining piles in water-rich strata foundation pit engineering. Background Technology

[0002] With the large-scale development of underground space, deep foundation pit projects in water-rich strata are increasingly being used in the construction of rail transit, integrated utility tunnels, and underground commercial complexes. SMW (Soil Mooring and Water Stopping) piles, as a support method that combines soil retention and water stopping functions, have become the mainstream support scheme for foundation pit projects in water-rich strata due to their convenient construction, economical cost, and strong adaptability. They are widely used in soft soil areas such as East and South my country.

[0003] Current SMW (Surface Mount Weave) pile design primarily relies on plane strain assumptions and limit equilibrium theory to determine support parameters. On one hand, traditional design neglects the coupling effect of seepage and stress fields in water-rich strata, leading to significant discrepancies between calculated pore pressure distribution and actual conditions. On the other hand, the determination of key parameters such as support stiffness and embedment depth largely depends on engineering experience, lacking systematic optimization methods. Engineering practice shows that SMW piles designed using traditional methods often exhibit actual deformation exceeding predicted values ​​by 20%–35%, while conservative design results in 15%–20% material waste. This economic and safety contradiction is particularly pronounced in deep foundation pits exceeding 15m in depth.

[0004] Based on the above analysis, it is necessary to study an optimization method for SMW retaining pile support parameters in water-rich strata foundation pit engineering. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method and system for optimizing the support parameters of SMW retaining piles in water-rich strata foundation pit engineering. By constructing a foundation pit excavation model, the influence of the stiffness of the support structure, the embedment depth, and the pre-applied axial force on the lateral displacement and heave deformation of the foundation pit is analyzed. Sensitivity analysis is used to quantify the support stiffness (E...). s I s The contribution weights of soil penetration depth (D) and pre-applied axial force (N) to deformation are determined based on a multi-objective optimization algorithm to solve for the δ... v ≤0.2%H and δ h The optimal solution set ≤0.1%H.

[0006] The present invention adopts the following technical solution: On one hand, the present invention provides a method for optimizing the support parameters of SMW retaining piles in foundation pit engineering in water-rich strata, including: S1. Obtain the excavation calculation model of the foundation pit project in water-rich strata under the support of SMW retaining piles. The support structure is composed of SMW retaining piles and cement-soil, and is characterized by an equivalent continuous wall. S2. Determine the physical and mechanical parameters of the water-rich soil to be excavated; S3. Determine the SMW retaining pile support structure parameters, including the SMW retaining pile support stiffness EsIs, the soil penetration depth D, and the pre-applied axial force N. S4. The water-rich stratum to be excavated is meshed, and the stress field control equation, seepage field control equation, the physical and mechanical parameters determined in step S2, the SMW retaining pile support structure parameters determined in step S3, the initial ground stress, and the initial pore pressure are input into the excavation calculation model. A convergence criterion is set for the excavation calculation model, and the excavated stratum stress σ' and pore pressure P are calculated and output. w、 seepage rate v w The bending moment M(z) of the equivalent continuous wall along the depth direction, where z represents the depth of the equivalent continuous wall; S5. Based on the output of step S4, calculate the bottom heave value of the foundation pit and the lateral deformation of the SMW retaining piles. S6. Repeatedly changing the stiffness E of the SMW retaining pile support. s I s The specific values ​​of the penetration depth D and the pre-applied axial force N are obtained by repeating steps S3-S5 to obtain the bottom heave value of the foundation pit and the lateral deformation of the SMW retaining piles under different support conditions, and a database is established. S7. Sensitivity analysis was used to quantify the SMW retaining pile support stiffness E. s I s The contribution weights of the soil penetration depth D and the pre-applied axial force N to the lateral deformation of the support and the heave deformation of the foundation pit; S8. Based on the contribution weights obtained in step S7, determine the optimal support scheme using a multi-objective optimization algorithm.

[0007] In addition to any of the possible implementations described above, another implementation is provided in which the method for obtaining the physical and mechanical parameters in step S2 is as follows: The dry density and void ratio of soil samples were determined by conventional tests. The effective internal friction angle ϕ, dilatation angle ψ, cohesion c, and reference secant modulus E were obtained through triaxial compression and shear tests. 50 ref Reference reloading modulus E ur ref Reference consolidation modulus E oed ref Stiffness stress level index m, reference initial shear modulus G oref ; The initial permeability coefficient k0 and the seepage-strain coupling coefficient α were obtained through variable head permeability tests and consolidation-permeability combined tests.

[0008] The initial ground stress and initial pore pressure are calculated based on the soil density and groundwater level.

[0009] In addition to any of the possible implementations described above, another implementation is provided in which, in step S1, the equivalent flexural stiffness EI of the equivalent continuous wall... eq : (1) Where: E s E c These are the elastic moduli of the SMW retaining piles and the elastic moduli of the cement-soil mixture, respectively; I s I c These are the moments of inertia of the SMW retaining piles and the moments of inertia of the cement-soil, respectively.

[0010] In addition to any of the possible implementations described above, another implementation is provided in which, in step S4, the stress field control equation is: (2) (3) Where Δσ' is the effective stress increment; σ' is the formation stress; ε is the formation strain; Δε is the formation strain increment; D ep G is the elastoplastic stiffness matrix; G is the shear modulus. (4) Where γ is the current calculated shear strain intensity; γ ref The characteristic shear strain is defined as the strain when G = 0.722G. o ref The corresponding shear strain controls the rate of stiffness decay; a and b are fitting parameters; The governing equation for the seepage field is: (5) (6) Where, ε v γ represents the bulk strain, calculated from the formation strain ε; k0 represents the initial permeability; k represents the permeability coefficient, obtained from the test calibration in step two; w γ represents the specific gravity of water. w =ρ w g, ρ w Where is the density of water, g is the acceleration due to gravity; α is the seepage-strain coupling coefficient; P w This refers to pore pressure.

[0011] In addition to any of the possible implementations described above, another implementation is provided in which, in step S4, the convergence criterion is strain increment < 1 × 10⁻⁶. 4 The pore pressure change is <0.1 kPa; the excavation calculation model is equipped with an implicit iterative algorithm and adopts adaptive mesh technology to dynamically densify the high stress gradient region, simulating the interaction between the retaining structure and groundwater seepage and soil deformation.

[0012] In addition to any of the possible implementations described above, another implementation is provided in which, in step S5, the bottom heave value of the foundation pit is calculated using the ground stress σ' after excavation and the constitutive relationship of the water-rich silty soil layer; the lateral deformation of the SMW retaining piles is calculated using the bending moment M(z) of the equivalent continuous wall along the depth direction and the equivalent bending stiffness EI. eq Calculated; (7) Where y represents the lateral deformation of the support; z represents the equivalent continuous wall depth.

[0013] In addition to any of the possible implementations described above, another implementation is provided in which, in step S7, Morris sensitivity analysis is used to quantify the SMW retaining pile stiffness E. s I s The contribution weights of the three factors—depth of penetration (D), and pre-applied axial force (N)—to the lateral deformation of the support and the heave deformation of the foundation pit are as follows: S71. Generate the Morris sampling matrix: Iterate through all parameters by changing one parameter at a time to form the basic effect value (EE) of each parameter. i ; (8) Among them, EE i For X i Basic effect value under the +Δ parameter group; Y(X i +Δ) is the Xth i +Δ parameter group: maximum value of lateral displacement or bottom heave of the foundation pit; Y(X i ) is the Xth i The maximum value of the lateral displacement or bottom heave of the foundation pit under the parameter set; Δ is the difference between the variables of the two parameter sets; the lateral displacement of the foundation pit and the lateral deformation of the support are coordinated and consistent, and their values ​​are equal; S72. Sensitivity index calculation: Basic effect value (EE) of the parameter i mean μ i Reflects the overall strength of the parameter's influence on the response; weight W i The weight of the parameter's influence is calculated using the mean weight: (9).

[0014] In addition to any of the possible implementations described above, another implementation is provided, wherein step S8 includes: S81. Optimization is performed using the NSGA-II multi-objective optimization algorithm. Objective function: (10) (11) Performance constraints: (12) (13) Boundary constraints: 0.8H ≤ D ≤ 1.5H(14) 50 ≤ E s I s ≤ 500 (MN·m 2 (15) 0.2N0 ≤ N ≤ 0.5N0(16) S82. For each group of candidate individuals generated by the NSGA-II algorithm, i.e., a group (E s I s Substitute the values ​​of δ, D, and N into the excavation calculation model established in step S1 to obtain the corresponding objective function value (δ). v , δ h ); S83. Repeat step S82 to obtain the Pareto optimal front curve. The horizontal axis of the optimal front curve represents the total support cost (in ten thousand yuan); the vertical axis represents the maximum lateral displacement of the foundation pit (in mm); each data point in the curve represents a set of (E s I s (,D, N) parameter combinations; S84. Based on construction costs and deformation control requirements, select the optimal set of support parameters (E) from the optimal front-line curve diagram in step S83. s I s , D, N).

[0015] On the other hand, the present invention also provides an optimization system for SMW retaining pile support parameters in water-rich strata foundation pit engineering. The system is used to implement the above-mentioned method and includes: The soil physical and mechanical parameter input module is used to input the physical and mechanical parameters of the water-rich soil to be excavated. These parameters include dry density, void ratio, effective internal friction angle ϕ, dilatation angle ψ, cohesion c, and reference secant modulus E. 50 ref Reference reloading modulus E urref Reference consolidation modulus E oed ref Stiffness stress level index m, reference initial shear modulus G o ref Initial permeability coefficient k0 and seepage-strain coupling coefficient α; The SMW retaining pile support structure parameter determination module is used to determine the parameters based on the SMW retaining pile support stiffness E. s I s Calculate the SMW retaining pile support structure parameters based on the soil penetration depth D and the pre-applied axial force N; The excavation calculation simulation module includes an excavation calculation model for a foundation pit project in a water-rich stratum supported by SMW retaining piles. This model is used to mesh the water-rich stratum to be excavated and inputs the stress field control equation, seepage field control equation, the physical and mechanical parameters, the SMW retaining pile support structure parameters, initial ground stress, and initial pore pressure into the excavation calculation model. Convergence criteria are set for the excavation calculation model, and the model calculates and outputs the ground stress σ' and pore pressure P after excavation. w、 seepage rate v w The bending moment M(z) of the equivalent continuous wall along the depth direction is calculated; and the bottom heave and lateral deformation of the foundation pit are calculated. Database of pit bottom heave and lateral deformation, based on different SMW retaining pile support stiffness E s I s Calculate the depth of penetration (D) and the pre-applied axial force (N), and store the corresponding bottom heave and lateral deformation of the foundation pit in the database. The weight determination module, based on the data in the database, uses sensitivity analysis to quantify the SMW retaining pile stiffness E. s I s The contribution weights of the soil penetration depth D and the pre-applied axial force N to the lateral deformation of the support and the heave deformation of the foundation pit; The parameter optimization module, based on the contribution weights and a multi-objective optimization algorithm, determines the optimal support scheme, which corresponds to the optimal SMW retaining pile support stiffness E. s I s , Depth of penetration into the soil D, Pre-applied axial force N.

[0016] In addition to any of the possible implementations described above, another implementation is provided, which uses Plaxis 3D finite element software to construct an excavation calculation model for a foundation pit project in water-rich strata under SMW retaining pile support.

[0017] The beneficial effects of this invention are as follows: 1. By constructing a fluid-solid coupling model of water-rich strata based on the HS-small constitutive relation, the excavation simulation calculation of foundation pit under SMW retaining pile support conditions was carried out, which solved the industry problem that traditional models could not simulate small strain stiffness and seepage effects, and improved the deformation prediction accuracy by more than 50%.

[0018] 2. Consider the influence of support stiffness, support depth, and pre-applied axial force on the lateral displacement of the support and the heave value at the bottom of the pit. Then, combine this with Morris sensitivity analysis to quantify the support stiffness (E). s I s The contribution weights of the penetration depth (D) and pre-applied axial force (N) to the lateral displacement and base heave deformation of the foundation pit were determined, clarifying the priority of optimization and upgrading the design from "experience-driven" to "data-driven". Based on the NSGA-II multi-objective optimization algorithm, the optimal SMW retaining pile support scheme for water-rich foundation pits was determined. Attached Figure Description

[0019] Figure 1 The diagram shown is a flowchart illustrating a method for optimizing the support parameters of SMW retaining piles in a water-rich stratum foundation pit project according to an embodiment of the present invention.

[0020] Figure 2 The diagram shown is a flowchart of the method for determining physical and mechanical parameters using the GDS testing device in this embodiment.

[0021] Figure 3 The flowchart shown is a Morris sensitivity analysis flowchart from an example.

[0022] Figure 4 The diagram shown is a flowchart of the calculation based on the NSGA-II multi-objective optimization algorithm in the embodiment.

[0023] Figure 5 The following is a model diagram of the foundation pit excavation in the water-rich stratum in the embodiment: (a) support structure; (b) retaining structure; (c) location of measuring points on the retaining structure.

[0024] Figure 6 The figure shown is a comparative analysis of the model and experiment in the embodiment. Detailed Implementation

[0025] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered in isolation, but can be combined with each other to achieve better technical effects.

[0026] like Figure 1 As shown in the figure, an embodiment of the present invention provides a method for optimizing the support parameters of SMW retaining piles in a foundation pit project in a water-rich stratum, comprising: S1. Obtain the excavation calculation model of the foundation pit project in water-rich strata under the support of SMW retaining piles. The support structure is composed of SMW retaining piles and cement-soil, and is characterized by an equivalent continuous wall. S2. Determine the physical and mechanical parameters of the water-rich soil to be excavated; S3. Determine the SMW retaining pile support structure parameters, including the SMW retaining pile support stiffness EsIs, the soil penetration depth D, and the pre-applied axial force N. S4. The water-rich stratum to be excavated is meshed, and the stress field control equation, seepage field control equation, the physical and mechanical parameters determined in step S2, the SMW retaining pile support structure parameters determined in step S3, the initial ground stress, and the initial pore pressure are input into the excavation calculation model. A convergence criterion is set for the excavation calculation model, and the excavated stratum stress σ' and pore pressure P are calculated and output. w、 seepage rate v w The bending moment M(z) of the equivalent continuous wall along the depth direction, where z represents the depth of the equivalent continuous wall; S5. Based on the output of step S4, calculate the bottom heave value of the foundation pit and the lateral deformation of the SMW retaining piles. S6. Repeatedly changing the stiffness E of the SMW retaining pile support. s I s The specific values ​​of the penetration depth D and the pre-applied axial force N are obtained by repeating steps S3-S5 to obtain the bottom heave value of the foundation pit and the lateral deformation of the SMW retaining piles under different support conditions, and a database is established. S7. Sensitivity analysis was used to quantify the SMW retaining pile support stiffness E. s I s The contribution weights of the soil penetration depth D and the pre-applied axial force N to the lateral deformation of the support and the heave deformation of the foundation pit; S8. Based on the contribution weights obtained in step S7, determine the optimal support scheme using a multi-objective optimization algorithm.

[0027] In one specific embodiment, in step S2, the method for obtaining the physical and mechanical parameters is as follows: The dry density and void ratio of soil samples were determined by conventional tests. The effective internal friction angle ϕ, dilatation angle ψ, cohesion c, and reference secant modulus E were obtained through triaxial compression and shear tests. 50 ref Reference reloading modulus E ur ref Reference consolidation modulus E oed ref Stiffness stress level index m, reference initial shear modulus G o ref ; The initial permeability coefficient k0 and the seepage-strain coupling coefficient α were obtained through variable head permeability tests and consolidation-permeability combined tests.

[0028] The initial ground stress and initial pore pressure are calculated based on the soil density and groundwater level.

[0029] In one specific embodiment, in step S1, the equivalent flexural stiffness EI of the equivalent continuous wall eq : (1) Where: E s E c These are the elastic moduli of the SMW retaining piles and the elastic moduli of the cement-soil mixture, respectively; I s I c These are the moments of inertia of the SMW retaining piles and the moments of inertia of the cement-soil, respectively.

[0030] The composite stiffness EI of SMW method piles eq The stiffness E of the SMW retaining piles is determined by the combined contribution of cement-soil mixing piles and internally inserted steel sections, based on the most flexible support conditions and engineering economics. s I s The value range is 50~500MN·m 2 The minimum embedment depth D is taken as 0.8H according to the "Technical Specification for Foundation Pit Support". In order to control deformation and meet the requirements for anti-piping, the maximum embedment depth D is 1.5H.

[0031] In one specific embodiment, in step S4, based on the HS-small constitutive relation, the stress field governing equation is constructed as follows: (2) (3) Where Δσ' is the effective stress increment; σ' is the formation stress; ε is the formation strain; Δε is the formation strain increment; D ep G is the elastoplastic stiffness matrix; G is the shear modulus. (4) The shear modulus G is corrected using a stiffness degradation model, which naturally considers the influence of shear history, clarifies the nonlinear variation characteristics of stiffness, and is more consistent with reality; γ is the current calculated shear strain strength; γ ref The characteristic shear strain is defined as the strain when G = 0.722G. o ref The corresponding shear strain controls the rate of stiffness decay; a and b are fitting parameters; G o ref For reference, the initial shear modulus; Combining Darcy's law, the governing equations for the seepage field are constructed as follows: (5) (6) Where, ε v γ represents the bulk strain, calculated from the formation strain ε; k0 represents the initial permeability; k represents the permeability coefficient, obtained from the test calibration in step two; w γ represents the specific gravity of water. w =ρ w g, ρ w Where is the density of water, g is the acceleration due to gravity; α is the seepage-strain coupling coefficient; P w This refers to pore pressure.

[0032] In one specific embodiment, in step S4, the convergence criterion is strain increment < 1 × 10⁻⁶. 4 The pore pressure change is <0.1 kPa; the excavation calculation model is equipped with an implicit iterative algorithm and adopts adaptive mesh technology to dynamically densify the high stress gradient region, simulating the interaction between the retaining structure and groundwater seepage and soil deformation.

[0033] In one specific embodiment, in step S5, the heave value at the bottom of the foundation pit is calculated using the ground stress σ' after excavation and the constitutive relation of the water-rich silt layer. The constitutive relation of the water-rich silt layer adopts the HS-small model to accurately simulate the small strain stiffness characteristics of the soil. The lateral deformation of the SMW retaining piles is calculated using the bending moment M(z) of the equivalent continuous wall along the depth direction and the equivalent bending stiffness EI. eq Calculated; (7) Where y represents the lateral deformation of the support; z represents the equivalent continuous wall depth.

[0034] In one specific embodiment, when establishing the database, the SMW retaining pile support stiffness E s I s (50~500MN·m) 2 A database was established to measure the bottom heave and lateral deformation of the support under varying penetration depths D (0.8~1.5H) and pre-applied axial force N (0.2~0.5N0). N0 represents the design value of the axial force of a single SMW pile support.

[0035] In one specific embodiment, in step S7, Morris sensitivity analysis is used to quantify the SMW retaining pile stiffness E. s I s The contribution weights of the three factors—depth of penetration (D), and pre-applied axial force (N)—to the lateral deformation of the support and the heave deformation of the foundation pit are as follows: S71. Generate the Morris sampling matrix: Iterate through all parameters by changing one parameter at a time to form the basic effect value (EE) of each parameter. i ; (8) Among them, EE i For X i Basic effect value under the +Δ parameter group; Y(X i +Δ) is the Xth i +Δ parameter group: maximum value of lateral displacement or bottom heave of the foundation pit; Y(X i ) is the Xth i The maximum value of the lateral displacement or bottom heave of the foundation pit under the parameter set; Δ is the difference between the variables of the two parameter sets; the lateral displacement of the foundation pit and the lateral deformation of the support are coordinated and consistent, and their values ​​are equal; S72. Sensitivity index calculation: Basic effect value (EE) of the parameter i mean μ i Reflects the overall strength of the parameter's influence on the response; weight W i The weight of the parameter's influence is calculated using the mean weight: (9).

[0036] When using the Morris sensitivity analysis method, sampling and calculation are performed within the range of values ​​for the optimization variables; the basic effects (EE) of each parameter are calculated. i The absolute mean (μ) of the design variables is used to quantify the influence intensity and nonlinear interaction effect of each design variable on the deformation response of the foundation pit; and further, through normalization, the contribution weight (W) of each design variable to deformation control is obtained. i Clearly define the primary and secondary order of parameter optimization.

[0037] In one specific embodiment, the support stiffness (E) s I s The depth of penetration (D) and the pre-applied axial force of the support (N) are used as optimization design variables; the maximum lateral displacement of the foundation pit (δ) is used as the optimization design variable. v ≤ 0.2%H) and the maximum heave value of the foundation pit (δ) h ≤ 0.1%H) is used as a deformation control constraint, where H is the excavation depth of the foundation pit; the constraint is determined according to the deformation control requirements for Class I foundation pits in the "Technical Specification for Foundation Pit Support" (JGJ120-2012).

[0038] In one specific embodiment, step S8 includes: S81. Optimization is performed using the NSGA-II multi-objective optimization algorithm. Objective function: (10) (11) Performance constraints: (12) (13) Boundary constraints: 0.8H ≤ D ≤ 1.5H(14) 50 ≤ E s I s ≤ 500 (MN·m 2 (15) 0.2N0 ≤ N ≤ 0.5N0(16) S82. For each group of candidate individuals generated by the NSGA-II algorithm, i.e., a group (E s I s Substitute the values ​​of δ, D, and N into the excavation calculation model established in step S1 to obtain the corresponding objective function value (δ). v , δ h ); S83. Repeat step S82 to obtain the Pareto optimal front curve. The horizontal axis of the optimal front curve represents the total support cost (in ten thousand yuan); the vertical axis represents the maximum lateral displacement of the foundation pit (in mm); each data point in the curve represents a set of (E s I s (,D, N) parameter combinations; S84. Based on construction costs and deformation control requirements, select the optimal set of support parameters (E) from the optimal front-line curve diagram in step S83. s I s , D, N).

[0039] In one specific embodiment, when initializing the population based on the NSGA-II multi-objective optimization algorithm, the algorithm generates more initial individuals in the search space with high weight parameters (such as the soil depth D), thereby improving the search efficiency and convergence speed of the algorithm.

[0040] This invention provides an optimization system for SMW retaining pile support parameters in foundation pit engineering in water-rich strata. The system is used to implement the above-described method and includes: The soil physical and mechanical parameter input module is used to input the physical and mechanical parameters of the water-rich soil to be excavated. These parameters include dry density, void ratio, effective internal friction angle ϕ, dilatation angle ψ, cohesion c, and reference secant modulus E. 50 ref Reference reloading modulus E ur ref Reference consolidation modulus Eoed ref Stiffness stress level index m, reference initial shear modulus G o ref Initial permeability coefficient k0 and seepage-strain coupling coefficient α; The SMW retaining pile support structure parameter determination module is used to determine the parameters based on the SMW retaining pile support stiffness E. s I s Calculate the SMW retaining pile support structure parameters based on the soil penetration depth D and the pre-applied axial force N; The excavation calculation simulation module includes an excavation calculation model for a foundation pit project in a water-rich stratum supported by SMW retaining piles. This model is used to mesh the water-rich stratum to be excavated and inputs the stress field control equation, seepage field control equation, the physical and mechanical parameters, the SMW retaining pile support structure parameters, initial ground stress, and initial pore pressure into the excavation calculation model. Convergence criteria are set for the excavation calculation model, and the model calculates and outputs the ground stress σ' and pore pressure P after excavation. w、 seepage rate v w The bending moment M(z) of the equivalent continuous wall along the depth direction is calculated; and the bottom heave and lateral deformation of the foundation pit are calculated. Database of pit bottom heave and lateral deformation, based on different SMW retaining pile support stiffness E s I s Calculate the depth of penetration (D) and the pre-applied axial force (N), and store the corresponding bottom heave and lateral deformation of the foundation pit in the database. The weight determination module, based on the data in the database, uses sensitivity analysis to quantify the SMW retaining pile stiffness E. s I s The contribution weights of the soil penetration depth D and the pre-applied axial force N to the lateral deformation of the support and the heave deformation of the foundation pit; The parameter optimization module, based on the contribution weights and a multi-objective optimization algorithm, determines the optimal support scheme, which corresponds to the optimal SMW retaining pile support stiffness E. s I s , Depth of penetration into the soil D, Pre-applied axial force N.

[0041] Example A deep foundation pit project for a subway station in the city center has an excavation depth of H = 36.0 m. Important underground pipelines and buildings exist around the pit, resulting in strict environmental protection requirements; the pit's safety level is Level 1. The stratum is mainly saturated silt, with a water table depth of approximately 14.60~14.70 m. The design employs a support system combining SMW (Surface Mount Welded Wrap) piles and concrete supports, with H700×300 steel sections inserted internally.

[0042] A calculation model for the excavation of a foundation pit in water-rich strata under SMW retaining pile support was established using the finite element software PLAXIS 3D. The model was designed with a horizontal dimension of 4 times the excavation width to eliminate boundary effects and a depth dimension of 2 times the excavation depth.

[0043] The soil constitutive relation was represented by the HS-small model, and the seepage field was represented by Darcy's law. The SMW method piles were modeled using a linear elastic model, and the equivalent stiffness was calculated according to the "Technical Specification for Foundation Pit Support" (JGJ 120-2012). The supports and structures were simulated using elastic rod elements, and the cross-sectional area and elastic modulus were input according to the actual material properties.

[0044] The model accurately simulates the following processes: initial ground stress balance → construction of SMW method piles → excavation to the first support bottom elevation → application of pre-applied axial force N → continued excavation to the bottom of the pit.

[0045] like Figure 2 As shown, the physical and mechanical properties of the soil in the foundation pit of the water-rich stratum were determined using the GDS test device.

[0046] 1. Obtain the groundwater level depth, pit bottom elevation, and aquifer thickness and depth in the area where the foundation pit is located, and calculate the sample collection radius: Where r is the sample collection radius; ξ is the proportionality coefficient; H1, H2 and H D These represent the location of the foundation pit, the location of the pit bottom, and the depth of the groundwater level, respectively; M is the thickness of the aquifer; k d is the formation permeability coefficient.

[0047] 2. Using the center of the foundation pit as a reference, select several soil sampling points within the sample collection radius. Each sample collection point should be 3-15 cm away from the ground surface to ensure that each sample has the same volume.

[0048] 3. Dry density, porosity, and internal friction angle of the soil at each sampling point were determined using conventional indoor tests. Then, triaxial drained shear, triaxial compression, permeability, and stress-permeability coupling tests were conducted on the remolded soil samples using a GDS testing apparatus to obtain the dilatation angle, reference compression modulus, bulk modulus, permeability coefficient, and seepage-strain coupling coefficient. The relevant model test parameters are shown in Table 1. Simulation calculations were performed on the excavation of a foundation pit in water-rich strata supported by SMW retaining piles to verify the effectiveness of the model. A refined three-dimensional model of the foundation pit excavation in water-rich strata was constructed using the Plaxis-3D finite element model, as shown below. Figure 5 As shown, the lateral deformation and surface settlement of the support structure during excavation under the above parameters are calculated and compared with the results of on-site monitoring. Figure 6 It can be seen that the lateral displacement of the foundation pit and the surface settlement during the excavation of the foundation pit in the water-rich stratum calculated by the calculation method of the present invention are in good agreement with the experimental results of field monitoring, indicating that the method of the present invention has high reliability.

[0049] refer to Figure 3 , Figure 3 This demonstrates the use of Morris sensitivity analysis to quantify support stiffness (E). s I s The contribution weights of the penetration depth (D) and the pre-applied axial force (N) to the lateral displacement and bottom heave of the foundation pit.

[0050] 1. Support stiffness E s I s =50~500 MN·m 2 The lateral displacement of the foundation pit and the amount of bottom heave under the support depth D=0.8H~1.5H and the pre-applied axial force N=0.2 N0~0.5 N0 are discretized.

[0051] 2. The Morris method was used to generate 40 sampling paths. Each path traversed all parameters by changing one factor at a time, and the total number of calculations was 40×(3+1)=160.

[0052] 3. For each parameter change along each path, calculate its EE according to its basic effect formula. i The value, the formula is: Among them, EE i For X i Basic effect value under the +Δ parameter group; Y(X i +Δi) is the Xth i +Δ parameter group: maximum value of lateral displacement or bottom heave of the foundation pit; Y(X i ) is the Xth i The parameter set represents the maximum value of the lateral displacement or bottom heave of the foundation pit; Δ is the difference between the two parameter sets.

[0053] 4. Calculate the absolute mean (μ) of all EE values ​​for each parameter. i ) and contribution weight W i : .

[0054] refer to Figure 4 , Figure 4 This demonstrates, based on sensitivity analysis, the lateral displacement (δ) h ) and basal uplift (δ vThe optimal support parameters for SMW retaining piles, determined based on the NSGA-II multi-objective optimization algorithm, are as follows: 1. Determine the optimization objective function of the NSGA-II algorithm: 2. The contribution weights (W) obtained from the Morris analysis i Given the following, determine the constraints of the optimization algorithm: 0.8H ≤ D ≤ 1.5H 50 ≤ E s I s ≤ 500 (MN·m 2 ) 0.2N0 ≤ N ≤ 0.5N0 3. Set the main algorithm parameters, including population size of 100, number of iterations of 50, crossover probability of 0.9, and mutation probability of 0.1. For each set of parameters generated by the algorithm, the numerical model established in S1 is called to calculate the objective function value.

[0055] 4. After the algorithm finishes running, it outputs a Pareto optimal solution set. This solution set clearly shows the trade-off between support parameters and pit deformation. Finally, designers can select the optimal support parameter scheme from this solution set based on the specific safety and economic requirements of the project.

[0056] While several embodiments of the present invention have been provided herein, those skilled in the art should understand that modifications can be made to these embodiments without departing from the spirit of the invention. The above embodiments are merely exemplary and should not be construed as limiting the scope of the invention.

Claims

1. A method for optimizing the parameters of SMW retaining pile support in foundation pit engineering in water-rich strata, characterized in that, The method includes: S1. Obtain the excavation calculation model of the foundation pit project in water-rich strata under the support of SMW retaining piles. The support structure is composed of SMW retaining piles and cement-soil, and is characterized by an equivalent continuous wall. S2. Determine the physical and mechanical parameters of the water-rich soil to be excavated; S3. Determine the SMW retaining pile support structure parameters, including the SMW retaining pile support stiffness EsIs, the soil penetration depth D, and the pre-applied axial force N. S4. The water-rich stratum to be excavated is meshed, and the stress field control equation, seepage field control equation, the physical and mechanical parameters determined in step S2, the SMW retaining pile support structure parameters determined in step S3, the initial ground stress, and the initial pore pressure are input into the excavation calculation model. A convergence criterion is set for the excavation calculation model, and the excavated stratum stress σ', pore pressure Pw, and seepage rate v are calculated and output. w The bending moment M(z) of the equivalent continuous wall along the depth direction, where z represents the depth of the equivalent continuous wall; S5. Based on the output of step S4, calculate the bottom heave value of the foundation pit and the lateral deformation of the SMW retaining piles. S6. Repeatedly changing the stiffness E of the SMW retaining pile support. s I s The specific values ​​of the penetration depth D and the pre-applied axial force N are obtained by repeating steps S3-S5 to obtain the bottom heave value of the foundation pit and the lateral deformation of the SMW retaining piles under different support conditions, and a database is established. S7. Sensitivity analysis was used to quantify the SMW retaining pile support stiffness E. s I s The contribution weights of the soil penetration depth D and the pre-applied axial force N to the lateral deformation of the support and the heave deformation of the foundation pit; S8. Based on the contribution weights obtained in step S7, determine the optimal support scheme using a multi-objective optimization algorithm.

2. The method for optimizing SMW retaining pile support parameters for foundation pit engineering in water-rich strata as described in claim 1, characterized in that, In step S2, the method for obtaining the physical and mechanical parameters is as follows: The dry density and void ratio of soil samples were determined by conventional tests. The effective internal friction angle ϕ, dilatation angle ψ, cohesion c, and reference secant modulus E were obtained through triaxial compression and shear tests. 50 ref Reference reloading modulus E ur ref Reference consolidation modulus E oed ref Stiffness stress level index m, reference initial shear modulus G o ref ; The initial permeability coefficient k0 and the seepage-strain coupling coefficient α were obtained through variable head permeability tests and consolidation-permeability combined tests.

3. The method for optimizing SMW retaining pile support parameters in foundation pit engineering in water-rich strata as described in claim 1, characterized in that, In step S1, the equivalent flexural stiffness EI of the equivalent continuous wall eq : （1） Where: E s E c These are the elastic moduli of the SMW retaining piles and the elastic moduli of the cement-soil mixture, respectively; I s I c These are the moments of inertia of the SMW retaining piles and the moments of inertia of the cement-soil, respectively.

4. The method for optimizing SMW retaining pile support parameters for foundation pit engineering in water-rich strata as described in claim 1, characterized in that, In step S4, the stress field governing equation is: (2) (3) Where Δσ' is the effective stress increment; σ' is the formation stress; ε is the formation strain; Δε is the formation strain increment; D ep G is the elastoplastic stiffness matrix; G is the shear modulus. (4) Where γ is the current calculated shear strain intensity; γ ref The characteristic shear strain is defined as the strain when G = 0.722G. o ref The corresponding shear strain controls the rate of stiffness decay; a and b are fitting parameters; G o ref For reference, the initial shear modulus; The governing equation for the seepage field is: (5) (6) Where, ε v γ represents the bulk strain, calculated from the formation strain ε; k0 represents the initial permeability; k represents the permeability coefficient, obtained from the test calibration in step two; w γ represents the specific gravity of water. w =ρ w g, ρ w Where is the density of water, g is the acceleration due to gravity; α is the seepage-strain coupling coefficient; P w This refers to pore pressure.

5. The method for optimizing SMW retaining pile support parameters for foundation pit engineering in water-rich strata as described in claim 1, characterized in that, In step S4, the convergence criterion is that the strain increment is <1×10⁻⁶. 4 The pore pressure change is <0.1 kPa; the excavation calculation model is equipped with an implicit iterative algorithm and adopts adaptive mesh technology to dynamically densify the high stress gradient region, simulating the interaction between the retaining structure and groundwater seepage and soil deformation.

6. The method for optimizing SMW retaining pile support parameters for foundation pit engineering in water-rich strata as described in claim 3, characterized in that, In step S5, the heave value at the bottom of the foundation pit is calculated using the ground stress σ' after excavation and the constitutive relationship of the water-rich silty soil layer; the lateral deformation of the SMW retaining piles is calculated using the bending moment M(z) of the equivalent continuous wall along the depth direction and the equivalent bending stiffness EI. eq Calculated; (7) Where y represents the lateral deformation of the support; z represents the equivalent continuous wall depth.

7. The method for optimizing SMW retaining pile support parameters for foundation pit engineering in water-rich strata as described in claim 1, characterized in that, In step S7, Morris sensitivity analysis is used to quantify the SMW retaining pile stiffness E. s I s The contribution weights of the three factors—depth of penetration (D), and pre-applied axial force (N)—to the lateral deformation of the support and the heave deformation of the foundation pit are as follows: S71. Generate the Morris sampling matrix: Iterate through all parameters by changing one parameter at a time to form the basic effect value (EE) of each parameter. i ; (8) Among them, EE i For X i Basic effect value under the +Δ parameter group; Y(X) i +Δ) is the Xth i +Δ parameter group: maximum value of lateral displacement or bottom heave of the foundation pit; Y(X i ) is the Xth i The maximum value of the lateral displacement of the foundation pit or the bottom heave of the foundation pit under the parameter set; Δ is the difference between the variables of the two parameter sets; the lateral displacement of the foundation pit and the lateral deformation of the support are coordinated and consistent, and their values ​​are equal; S72. Sensitivity index calculation: Basic effect value (EE) of the parameter i mean μ i Reflects the overall strength of the parameter's influence on the response; weight W i The weight of the parameter's influence is calculated using the mean weight: (9)。 8. The method for optimizing SMW retaining pile support parameters for foundation pit engineering in water-rich strata as described in claim 1, characterized in that, Step S8 includes: S81. Optimization is performed using the NSGA-II multi-objective optimization algorithm. Objective function: (10) (11) Performance constraints: (12) (13) Boundary constraints: 0.8H ≤ D ≤ 1.5H(14) 50 ≤ E s AND s ≤ 500 (MN m 2 )(15) 0.2N0 ≤ N ≤ 0.5N0(16) S82. For each group of candidate individuals generated by the NSGA-II algorithm, i.e., a group (E s I s Substitute the values ​​of δ, D, and N into the excavation calculation model established in step S1 to obtain the corresponding objective function value (δ). v , δ h ); S83. Repeat step S82 to obtain the Pareto optimal front curve. The horizontal axis of the optimal front curve represents the total support cost (in ten thousand yuan); the vertical axis represents the maximum lateral displacement of the foundation pit (in mm); each data point in the curve represents a set of (E s I s (, D, N) parameter combinations; S84. Based on construction costs and deformation control requirements, select the optimal set of support parameters (E) from the optimal front-line curve diagram in step S83. s I s , D, N).

9. A parameter optimization system for SMW retaining pile support in foundation pit engineering in water-rich strata, characterized in that, The system is used to implement the method as described in any one of claims 1-8, the system comprising: The soil physical and mechanical parameter input module is used to input the physical and mechanical parameters of the water-rich soil to be excavated. These parameters include dry density, void ratio, effective internal friction angle ϕ, dilatation angle ψ, cohesion c, and reference secant modulus E. 50 ref Reference reloading modulus E ur ref Reference consolidation modulus E oed ref Stiffness stress level index m, reference initial shear modulus G o ref Initial permeability coefficient k0 and seepage-strain coupling coefficient α; The SMW retaining pile support structure parameter determination module is used to determine the parameters based on the SMW retaining pile support stiffness E. s I s Calculate the SMW retaining pile support structure parameters based on the soil penetration depth D and the pre-applied axial force N; The excavation calculation simulation module includes an excavation calculation model for a foundation pit project in a water-rich stratum supported by SMW retaining piles. This model is used to mesh the water-rich stratum to be excavated and inputs the stress field control equation, seepage field control equation, the physical and mechanical parameters, the SMW retaining pile support structure parameters, initial ground stress, and initial pore pressure into the excavation calculation model. Convergence criteria are set for the excavation calculation model, and the model calculates and outputs the ground stress σ' and pore pressure P after excavation. w、 seepage rate v w The bending moment M(z) of the equivalent continuous wall along the depth direction is calculated; and the bottom heave and lateral deformation of the foundation pit are calculated. Database of pit bottom heave and lateral deformation, based on different SMW retaining pile support stiffness E s I s Calculate the depth of penetration (D) and the pre-applied axial force (N), and store the corresponding bottom heave and lateral deformation of the foundation pit in the database. The weight determination module, based on the data in the database, uses sensitivity analysis to quantify the SMW retaining pile stiffness E. s I s The contribution weights of the soil penetration depth D and the pre-applied axial force N to the lateral deformation of the support and the heave deformation of the foundation pit; The parameter optimization module, based on the contribution weights and a multi-objective optimization algorithm, determines the optimal support scheme, which corresponds to the optimal SMW retaining pile support stiffness E. s I s , Depth of penetration into the soil D, Pre-applied axial force N.

10. The SMW retaining pile support parameter optimization system for foundation pit engineering in water-rich strata as described in claim 9, characterized in that, A calculation model for excavation under SMW retaining pile support in a foundation pit project in water-rich strata was constructed using Plaxis 3D finite element software.

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