A Method and System for Predicting Settlement of Existing Railway Subgrade During Excavation Based on Water Pressure

Abstract

This invention discloses a method and system for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure. The method includes: S100, constructing a three-dimensional fluid-structure interaction numerical model and setting boundary conditions for soil constitutive relations, initial pore water pressure field, and initial ground stress field; S200, calculating the dissipation process and dynamic distribution of pore water pressure inside and outside the foundation pit under different construction stages, as well as the spatial drop surface of groundwater level; S300, performing fluid-structure dynamic coupling solution with the actual dynamic load and the updated pore water pressure field and effective stress state of the soil at the current construction stage to calculate the additional stress field of the stratum under dynamic and static loads; S400, superimposing dynamic deformation and displacement data of adjacent composite foundation and underlying soil under each excavation and dewatering stage; S500, generating settlement prediction curves of existing railway subgrade that vary with time and space, and outputting the final quantitative settlement prediction index. This improves the accuracy and reliability of settlement prediction under complex hydrogeological conditions.

Description

Technical Field

[0001] This invention belongs to the field of water pressure monitoring technology, and more specifically, relates to a method and system for predicting the settlement of existing railway subgrade during foundation pit excavation based on water pressure. Background Technology

[0002] Excavation work near existing railway lines is a major technical challenge in modern construction. During excavation, especially when groundwater is extracted from subway pits near wide-station composite foundations for high-speed railways, the drop in groundwater level leads to dissipation of pore water pressure and increased effective stress in the surrounding soil. This causes settlement of the adjacent composite foundation and compression of the underlying soil, resulting in a significant increase in the overall settlement of the composite foundation. Simultaneously, the unloading of soil caused by excavation disrupts the original stress balance of the strata. This disturbance is directly transmitted to the adjacent existing railway line, easily causing displacement, settlement, and uneven deformation of the rails and roadbed, seriously threatening the safe operation of railway trains.

[0003] Extensive research and numerous engineering case studies have been conducted both domestically and internationally to address issues such as composite foundation settlement caused by excavation pit dewatering, as well as track displacement and deformation control. Current technologies primarily focus on the design of excavation pit support systems and the study of the dynamic response of track structures and subgrades. In practical engineering analysis, conventional methods typically involve stability calculations and deformation control of the excavation pit's support structure itself. However, when dealing with the impact of train operation on the excavation pit, researchers and engineers mostly employ simplified mechanical models, primarily by converting complex train dynamic loads into equivalent additional static loads superimposed on the soil to assess their force on the excavation pit support structure.

[0004] However, existing analytical methods and prediction techniques still have significant limitations. First, most existing technologies isolate railway traffic engineering and deep foundation pit engineering for independent analysis, rarely considering the comprehensive impact of the excavation process on adjacent existing track and subgrade during the foundation pit design stage, and lacking detailed and specific coupling effect analysis. Second, the practice of simply equating train dynamic loads to static loads is too idealistic and ignores the complex characteristics of real dynamic loads. Most importantly, the current prediction system for subgrade settlement directly induced by foundation pit excavation and dewatering is still incomplete, related research lacks systematicity, and there are few prediction methods that can accurately couple the relationship between water pressure changes and subgrade dynamic settlement, making it difficult to meet the refined requirements for safety protection of existing railways under complex geological and high-speed rail conditions. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a method and system for predicting the settlement of existing railway subgrade during foundation pit excavation based on water pressure. By constructing a three-dimensional fluid-structure interaction model that includes the foundation pit, composite foundation, and existing railway line, the method organically combines the dissipation of pore water pressure caused by foundation pit dewatering, the unloading effect of soil excavation, and the dynamic load generated by train operation. This enables a holistic system analysis of the settlement of existing railway subgrade under the multi-field coupling effect of water, soil, and dynamic loads, significantly improving the accuracy and reliability of settlement prediction under complex hydrogeological conditions.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a method for predicting the settlement of existing railway subgrade during foundation pit excavation based on water pressure is provided, specifically including the following steps:

[0007] S100. Construct a three-dimensional fluid-structure interaction numerical model and set the boundary conditions for soil constitutive relations, initial pore water pressure field and initial geostress field of strata.

[0008] S200. Simultaneously simulate the groundwater pumping and soil excavation unloading process in the numerical model. Utilize the seepage control equation to calculate in real time the dissipation process, dynamic distribution, and spatial drop surface of the groundwater level inside and outside the foundation pit under different construction stages.

[0009] S300. Establish the transient excitation force function of existing line train operation to characterize the real dynamic load, and perform fluid-structure dynamic coupling solution with the updated pore water pressure field and soil effective stress state in the current construction stage to calculate the additional stress field of the stratum under the combined action of dynamic and static loads.

[0010] S400, extract additional stress and pore water pressure dissipation, calculate the consolidation compression of the soil around the foundation pit due to the increase in effective stress, and superimpose the dynamic deformation and displacement data of the adjacent composite foundation and underlying soil at each excavation and dewatering stage.

[0011] S500 calculates and extracts the cumulative settlement and uneven deformation of the existing railway subgrade during the entire excavation and dewatering cycle, generates a settlement prediction curve of the existing subgrade that varies with time and space, and outputs the final quantitative index of settlement prediction.

[0012] Furthermore, in the three-dimensional fluid-structure interaction numerical model, for saturated soil, the mutual influence between groundwater seepage and soil deformation during the excavation of the foundation pit is considered. The small deformation and quasi-static assumptions are adopted to establish three-dimensional fluid-structure interaction control equations, including equilibrium equations, effective stress principle and seepage continuity equations.

[0013] Furthermore, the equilibrium equation is used to describe the static equilibrium relationship of soil under stress, that is, the spatial variation of the total stress inside the soil is balanced with the volume force, specifically:

[0014] ;

[0015] in, The Hamiltonian operator represents the spatial derivative operation.

[0016] The total stress tensor of the soil reflects the total force acting on a unit area of ​​the soil.

[0017] This is a volume force vector, including the soil's self-weight, with the vertically downward direction being positive.

[0018] The principle of effective stress is as follows: During the excavation and dewatering of the foundation pit, the soil is subjected to two forces: effective stress and pore water pressure. Effective stress is the key factor determining soil deformation and strength, and the relationship between the two is as follows:

[0019] ;

[0020] in, This is the effective stress tensor of the soil, which is the stress that actually acts on the contact surface of soil particles after deducting pore water pressure from the total stress.

[0021] This refers to pore water pressure, which is the pressure exerted on the water within the pores of the soil.

[0022] It is a unit tensor, used to ensure dimensionality consistency in tensor operations;

[0023] The seepage continuity equation is used to describe the continuity of groundwater seepage during the dewatering process of foundation pits. Specifically, the difference between the amount of water flowing into and out of a soil unit per unit time is equal to the change in pore water volume within that unit.

[0024] ;

[0025] in, The soil permeability tensor reflects the soil's ability to allow groundwater to seep through; different soil layers have different permeability coefficients.

[0026] For the Laplace operator,

[0027] The density of water,

[0028] This represents the volumetric strain of the soil, which is the ratio of the change in soil volume to the initial volume.

[0029] This refers to the construction period.

[0030] Furthermore, the boundary conditions include displacement boundaries and seepage boundaries;

[0031] The displacement boundaries are as follows: the bottom of the model is subject to fixed constraints to prevent unreasonable settlement or heave of the bottom soil; the sides of the model are subject to normal constraints to simulate the constraint effect of infinitely extended strata in actual engineering, which is achieved by setting numerical model parameters.

[0032] The seepage boundary is defined as follows: the natural ground surface is the permeable boundary, the initial groundwater level is the constant head boundary, the dewatering well is the constant flow or constant drawdown boundary, and the sides and bottom of the model are the impermeable boundaries.

[0033] Furthermore, in step S200, when calculating the external pore water pressure within the foundation pit, the finite element method is used to iteratively solve the seepage continuity equation based on the excavation unloading and dewatering conditions of each construction step. This allows for real-time calculation of the dissipation process, dynamic distribution, and groundwater level drop surface of the pore water pressure inside and outside the foundation pit at different construction stages. The finite element iteration formula is as follows:

[0034] ;

[0035] in, This is a permeability matrix, reflecting the influence of soil permeability characteristics on seepage.

[0036] Let be the pore water pressure vector at time t+Δt.

[0037] The seepage boundary load vector is determined by the seepage boundary conditions.

[0038] For water storage matrix,

[0039] Let be the pore water pressure vector at time t.

[0040] The time step is consistent with the time interval of the discretization of the construction steps;

[0041] In practice, the above formula is embedded into the model, and transient seepage iterations are performed for each construction step to output the pore water pressure values ​​at different locations inside and outside the foundation pit at each moment. Then, pore water pressure cloud maps and groundwater level drop contour surfaces are plotted, and the dissipation rate of excess pore water pressure is calculated. The dynamic variation of pore water pressure with construction time and spatial location was clarified.

[0042] Furthermore, in step S300, since the train's wheels generate transient dynamic loads when in contact with the track, and these loads vary with time and space, they need to be simplified into a sequence of moving concentrated loads. A transient excitation force function is then established to characterize the magnitude, frequency, and movement characteristics of the actual dynamic load. When establishing the transient excitation force function, the train load is simplified to a moving concentrated load, and the magnitude of its transient excitation force is related to the train's axle load and speed, specifically:

[0043] ;

[0044] in, Let be the transient excitation force of the train at time t.

[0045] This is the static load on a single axle of the train, determined by the axle load of the train, and equal to the axle load value.

[0046] Let be the influence function of dynamic load.

[0047] The dynamic load influence function Used to characterize the influence of train speed and position on the excitation force, its value is related to the train speed. and the position of train load Related.

[0048] Furthermore, the train travels at a constant speed along the existing line, and its horizontal position changes linearly with time, i.e., the position where the train load is applied. for:

[0049] ;

[0050] in, For a moment Horizontal position coordinates of the train load

[0051] These are the initial position coordinates of the train;

[0052] In actual train operation, due to factors such as track irregularities and wheel wear, the dynamic load will be greater than the static load, necessitating the introduction of a dynamic load factor. After correction, the actual dynamic load acting on the roadbed surface is obtained, specifically:

[0053] ;

[0054] in, The corrected transient dynamic load for the train.

[0055] The dynamic load coefficient It is determined based on the existing railway operation and on-site test data.

[0056] Furthermore, under the action of train dynamic load, soil deformation and groundwater seepage will have dynamic interaction, and it is necessary to establish fluid-structure dynamic coupling equations to combine dynamic load, excavation unloading statics, and pore water pressure changes for coupled solution, including displacement equilibrium equations and seepage continuity equations.

[0057] The displacement equilibrium equation is used to describe the dynamic equilibrium relationship of soil under the combined action of dynamic and static loads, taking into account the effects of inertial force and damping force, specifically:

[0058] ;

[0059] in, The soil mass matrix, calculated from parameters such as soil density and element volume, reflects the inertial properties of the soil.

[0060] Let be the soil acceleration vector.

[0061] This is the soil damping matrix, which reflects the energy dissipation during soil vibration.

[0062] Let be the soil velocity vector.

[0063] This is the soil stiffness matrix, reflecting the elastic deformation characteristics of the soil.

[0064] Let be the soil displacement vector.

[0065] This is the fluid-structure interaction matrix, reflecting the effect of pore water pressure on soil deformation.

[0066] The pore water pressure vector.

[0067] The train dynamic load vector is given by The conversion yields the result; This is a static load vector, including the soil's self-weight and the unloading stress from the foundation pit excavation. Static forces included;

[0068] The seepage continuity equation is used to describe the continuity of groundwater seepage under dynamic loads, considering the influence of soil deformation on seepage, specifically:

[0069] ;

[0070] in, The seepage stiffness matrix is ​​calculated from the soil permeability coefficient k.

[0071] The pore water pressure vector.

[0072] For water storage matrix,

[0073] Let be the vector of the rate of change of pore water pressure.

[0074] Fluid-structure interaction matrix The transpose of the matrix, with dimensions equal to... on the contrary,

[0075] Let be the soil velocity vector.

[0076] The seepage flow vector is the pumping rate from the dewatering well. Sure.

[0077] Furthermore, in step S500, the roadbed settlement prediction curve includes a time-settlement curve, a spatial settlement cloud map, and a depth-settlement curve;

[0078] When generating the subgrade settlement prediction curve, data processing software is used to fit and interpolate the summarized settlement data to generate the above three types of settlement prediction curves.

[0079] Then, all calculation results are summarized, and four core quantitative indicators are extracted as the final output for the settlement prediction of existing railway subgrade. These indicators include: maximum cumulative settlement. Maximum uneven settlement Maximum inclination and settling rate ;

[0080] The settling rate The settlement-time curve is derived to reflect the rate of subgrade settlement. When the settlement rate approaches 0, the subgrade settlement reaches a stable state.

[0081] According to a second aspect of the present invention, a system for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure is provided, comprising:

[0082] Data acquisition module: used to construct a three-dimensional fluid-structure interaction numerical model and set the boundary conditions for soil constitutive relations, initial pore water pressure field and initial geostress field of strata;

[0083] Data simulation module: used to simultaneously simulate the groundwater pumping and soil excavation unloading process in the numerical model, and to calculate in real time the dissipation process, dynamic distribution and spatial drop surface of pore water pressure inside and outside the foundation pit under different construction stages using the seepage control equation.

[0084] Coupled solution module: used to establish the transient excitation force function of existing line train operation to characterize the real dynamic load, and perform fluid-structure dynamic coupling solution with the updated pore water pressure field and soil effective stress state of the current construction stage to calculate the additional stress field of the stratum under the combined action of dynamic and static loads.

[0085] Displacement calculation module: used to extract additional stress and pore water pressure dissipation, calculate the consolidation compression of the soil around the foundation pit due to the increase in effective stress, and superimpose the dynamic deformation and displacement data of the adjacent composite foundation and underlying soil at each excavation and dewatering stage.

[0086] Prediction output module: used to calculate and extract the cumulative settlement and uneven deformation of the existing railway subgrade during the entire excavation and dewatering cycle, generate the settlement prediction curve of the existing subgrade that varies with time and space, and output the final quantitative index of settlement prediction.

[0087] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0088] 1. The existing railway subgrade settlement prediction method of the present invention constructs a three-dimensional fluid-structure interaction model including the foundation pit, composite foundation and existing railway line, which organically combines the pore water pressure dissipation caused by foundation pit dewatering, the soil excavation unloading effect and the dynamic load generated by train operation, to achieve a holistic system analysis of the settlement of existing railway subgrade under the multi-field coupling effect of water-soil-dynamic load, which significantly improves the accuracy and reliability of settlement prediction under complex hydrogeological conditions.

[0089] 2. The existing railway subgrade settlement prediction method of the present invention accurately calculates the soil consolidation compression caused by the decrease in pore water pressure by simulating the seepage field changes and effective stress redistribution during the precipitation process in real time. Combined with the constitutive model of hardened soil, it effectively solves the problem of the underestimation of settlement of composite foundations in wide station yards of high-speed railways under precipitation conditions due to neglecting water pressure changes.

[0090] 3. The existing track subgrade settlement prediction method of the present invention establishes a transient excitation force function based on train axle load, speed and excitation frequency, and implements time history loading, which truly restores the high-frequency cyclic action of the train on the subgrade soil. It not only reflects the transient elastic deformation induced by dynamic load, but also captures the cumulative plastic deformation of the soil under the superposition of dynamic and static loads, effectively avoiding the deviation of the static equivalent method in predicting the long-term operational stability of the subgrade.

[0091] 4. The existing line subgrade settlement prediction method of the present invention extracts displacement data of characteristic nodes at different construction stages to generate settlement history curves that change over time and settlement trough curves that are distributed spatially. It can not only predict the final settlement amount, but also identify the settlement rate abrupt change points and the peak areas of longitudinal uneven deformation. This provides intuitive and quantitative data support for engineering designers to optimize the dewatering rate, adjust the excavation sequence, and formulate targeted reinforcement measures. Attached Figure Description

[0092] Figure 1 This is a flowchart illustrating a method for predicting the settlement of existing railway subgrade during foundation pit excavation based on water pressure, according to an embodiment of the present invention.

[0093] Figure 2 This is a cross-sectional view of the foundation pit excavation construction of a method for predicting the settlement of existing railway subgrade during foundation pit excavation based on water pressure, according to an embodiment of the present invention. Detailed Implementation

[0094] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0095] Example 1

[0096] like Figure 1-2 As shown, this embodiment of the invention provides a method for predicting the settlement of existing railway subgrade during foundation pit excavation based on water pressure, specifically including the following steps:

[0097] S100. Obtain geological survey data of the construction area, design parameters for dewatering of the foundation pit and parameters of the existing railway structure, construct a three-dimensional fluid-structure coupling numerical model including the foundation pit, composite foundation and existing line, and set the boundary conditions for soil constitutive relation, initial pore water pressure field and initial ground stress field of the strata.

[0098] S200. Based on the foundation pit dewatering scheme and the layered excavation sequence, the groundwater pumping and soil excavation unloading process are simulated synchronously in the numerical model. The seepage control equation is used to calculate in real time the dissipation process, dynamic distribution and spatial drop surface of the pore water pressure inside and outside the foundation pit under different construction stages.

[0099] S300. Establish the transient excitation force function of existing line train operation to characterize the real dynamic load, apply it to the roadbed surface, and perform fluid-structure dynamic coupling solution with the updated pore water pressure field and soil effective stress state of the current construction stage to calculate the additional stress field of the stratum under the combined action of dynamic and static loads.

[0100] S400, extract additional stress and pore water pressure dissipation, calculate the consolidation compression of the soil around the foundation pit due to the increase in effective stress, and superimpose the lateral and vertical displacement of the soil caused by the unloading of the foundation pit to obtain the dynamic deformation and displacement data of the adjacent composite foundation and the underlying soil under each excavation and dewatering stage.

[0101] S500 summarizes soil compression and deformation displacement data at different depths, calculates and extracts the cumulative settlement and uneven deformation of the existing railway subgrade during the entire excavation and dewatering cycle, generates settlement prediction curves of the existing subgrade that vary with time and space, and outputs the final quantitative indicators of settlement prediction.

[0102] In step S100, when obtaining geological survey data, it is necessary to clarify the soil layering situation, thickness of each soil layer, natural unit weight of soil, permeability coefficient, compression modulus, internal friction angle, cohesion, void ratio and other physical and mechanical parameters of the soil in the construction area; when obtaining the design parameters for foundation pit dewatering, it is necessary to determine the specific well location coordinates, well depth, single well pumping volume, target water level and duration of dewatering; when obtaining the structural parameters of existing railway, it is necessary to record the track type, roadbed height, roadbed width, train axle load, train speed, roadbed foundation type and key parameters of composite foundation.

[0103] In the three-dimensional fluid-structure interaction numerical model, for saturated soil, the mutual influence between groundwater seepage and soil deformation during the foundation pit excavation process is considered. The small deformation and quasi-static assumptions are adopted to establish the three-dimensional fluid-structure interaction control equations, including the equilibrium equation, the effective stress principle and the seepage continuity equation.

[0104] The equilibrium equations are used to describe the static equilibrium relationship of soil under stress, that is, the spatial variation of total stress within the soil is balanced with the volume forces, specifically:

[0105] ;

[0106] in, The Hamiltonian operator represents the spatial derivative operation.

[0107] The total stress tensor of the soil reflects the total force acting on a unit area of ​​the soil.

[0108] This is a volume force vector, including the soil's self-weight, with the vertically downward direction being positive.

[0109] The principle of effective stress is as follows: During the excavation and dewatering of the foundation pit, the soil is subjected to two forces: effective stress and pore water pressure. Effective stress is the key factor determining soil deformation and strength, and the relationship between the two is as follows:

[0110] ;

[0111] in, This is the effective stress tensor of the soil, which is the stress that actually acts on the contact surface of soil particles after deducting pore water pressure from the total stress.

[0112] This refers to pore water pressure, which is the pressure exerted on the water within the pores of the soil.

[0113] It is a unit tensor, used to ensure dimensionality consistency in tensor operations;

[0114] The seepage continuity equation is used to describe the continuity of groundwater seepage during the dewatering process of foundation pits. Specifically, the difference between the amount of water flowing into and out of a soil unit per unit time is equal to the change in pore water volume within that unit.

[0115] ;

[0116] in, The soil permeability tensor reflects the soil's ability to allow groundwater to seep through; different soil layers have different permeability coefficients.

[0117] For the Laplace operator,

[0118] The density of water,

[0119] This represents the volumetric strain of the soil, which is the ratio of the change in soil volume to the initial volume.

[0120] This refers to the construction period.

[0121] In setting the constitutive relation of soil, in order to truly reflect the deformation characteristics of soil during excavation unloading and water pressure changes, an elastoplastic constitutive model is adopted, and the transformation law of soil from elastic state to plastic state is described by yield function and flow law.

[0122] The yield function is used to determine whether the soil has reached the plastic yield state. When the yield function value is 0, the soil begins to undergo plastic deformation, specifically:

[0123] ;

[0124] in, Let be the yield function.

[0125] For the effective stress tensor of the soil,

[0126] The internal friction angle of the soil.

[0127] For soil cohesion,

[0128] The internal friction angle of the soil Cohesion of soil Together they determine the shear strength of the soil;

[0129] The flow rule is used to describe the development direction of plastic strain after the soil reaches yield, specifically:

[0130] ;

[0131] in, For the plastic strain increment tensor,

[0132] The plasticity multiplier is used to characterize the degree of development of plastic strain.

[0133] Let be the plastic potential function, and take... .

[0134] The initial geostress field is generated by the soil's own weight, and the initial geostress in the vertical and horizontal directions is as follows:

[0135] ;

[0136] in, The initial total vertical stress is linearly distributed along the depth direction.

[0137] The natural density of the soil.

[0138] To calculate the burial depth,

[0139] The initial horizontal total stress,

[0140] This is the coefficient of pressure on the stationary side;

[0141] In the initial pore water pressure field, the pore water pressure is in equilibrium with the groundwater level. Pore water pressure exists in the soil below the groundwater level, and the pore water pressure in the soil above the groundwater level is 0. Specifically:

[0142] ;

[0143] in, The initial pore water pressure,

[0144] The density of water,

[0145] To calculate the burial depth,

[0146] This represents the initial groundwater level depth.

[0147] The boundary conditions include displacement boundaries and seepage boundaries. The displacement boundaries are as follows: the bottom of the model is subject to fixed constraints to prevent unreasonable settlement or heave of the bottom soil; the sides of the model are subject to normal constraints to simulate the constraint effect of infinitely extended strata in actual engineering through numerical model parameter settings; the seepage boundaries are as follows: the natural ground surface is the permeable boundary, the initial groundwater level is the constant head boundary, the dewatering well is the constant flow or constant drawdown boundary, and the sides and bottom of the model are the impermeable boundaries.

[0148] In step S200, since the excavation and dewatering of the foundation pit are carried out in stages and steps, in order to accurately simulate the water pressure and deformation changes in each construction stage, the entire construction cycle needs to be discretized into N consecutive construction steps. Each construction step corresponds to a specific excavation depth and dewatering duration. The discretization expression is as follows:

[0149] ;

[0150] in, For construction time,

[0151] These are the end times of the 1st, 2nd, ..., Nth construction steps, respectively.

[0152] N represents the total number of construction steps, which are reasonably divided according to the number of excavation layers and dewatering stages to ensure that the excavation thickness and dewatering duration of each construction step conform to the actual construction plan.

[0153] During the soil excavation and unloading process, the soil's self-weight is unloaded. Each excavation step removes soil at a corresponding depth, reducing the self-weight pressure on the surrounding soil. The self-weight of the removed soil needs to be converted into an equivalent unloading stress and applied to the model excavation surface to simulate the unloading effect. The increment of the unloading stress is:

[0154] ;

[0155] in, To increase the excavation unloading stress,

[0156] This refers to the excavation thickness for this construction step.

[0157] When simulating it in the numerical model, delete the soil elements in the excavation area corresponding to the construction step, and apply a size of [value missing] to the excavation face. The equivalent unloading stress in the upward direction is used to simulate the excavation unloading process, ensuring that the unloading range and unloading stress of each construction step are consistent with the actual excavation situation.

[0158] Dewatering of the foundation pit lowers the groundwater level by pumping out groundwater. In the numerical model, based on the dewatering design parameters, corresponding flow boundaries are applied at the locations of the dewatering wells to simulate the groundwater pumping process, while simultaneously updating the spatial distribution of the groundwater level in real time. Specifically:

[0159] First, based on the single-well pumping rate designed for dewatering, the pumping rate of each dewatering well node is set to be constant, i.e. ,in Let be the pumping rate of the dewatering well at time t. Design the pumping capacity per well for precipitation;

[0160] Then, the groundwater level space is updated. As groundwater is pumped out, the groundwater level will gradually decrease, forming a spatially distributed descending surface, thus obtaining the groundwater level depth.

[0161] ;

[0162] in, Let be the depth of the groundwater level at time t and coordinates (x, y).

[0163] (x,y) are planar coordinates.

[0164] This represents the initial groundwater level depth.

[0165] The value of the groundwater level drop at time t and coordinates (x, y) is calculated from the seepage during the groundwater pumping process.

[0166] When calculating the external pore water pressure in the foundation pit, the finite element method is used to iteratively solve the seepage continuity equation in conjunction with the excavation unloading and dewatering conditions of each construction step. This allows for real-time calculation of the dissipation process, dynamic distribution, and groundwater level drop surface of the pore water pressure inside and outside the foundation pit at different construction stages. The finite element iterative formula is as follows:

[0167] ;

[0168] in, This is a permeability matrix, reflecting the influence of soil permeability characteristics on seepage.

[0169] Let be the pore water pressure vector at time t+Δt.

[0170] The seepage boundary load vector is determined by the seepage boundary conditions.

[0171] For water storage matrix,

[0172] Let be the pore water pressure vector at time t.

[0173] The time step is consistent with the time interval of the discretization of the construction steps;

[0174] In practice, the above formula is embedded into the model, and transient seepage iterations are performed for each construction step to output the pore water pressure values ​​at different locations inside and outside the foundation pit at each moment. Then, pore water pressure cloud maps and groundwater level drop contour surfaces are plotted, and the dissipation rate of excess pore water pressure is calculated. The dynamic variation of pore water pressure with construction time and spatial location was clarified.

[0175] In step S300, since the train's wheels generate transient dynamic loads when in contact with the track, and these loads vary with time and space, they need to be simplified into a sequence of moving concentrated loads. A transient excitation force function is then established to characterize the magnitude, frequency, and movement characteristics of the actual dynamic load. When establishing the transient excitation force function, the train load is simplified to a moving concentrated load, and the magnitude of its transient excitation force is related to the train's axle load and speed, specifically:

[0176] ;

[0177] in, Let be the transient excitation force of the train at time t.

[0178] This is the static load on a single axle of the train, determined by the axle load of the train, and equal to the axle load value.

[0179] Let be the influence function of dynamic load.

[0180] The dynamic load influence function Used to characterize the influence of train speed and position on the excitation force, its value is related to the train speed. and the position of train load Related.

[0181] The train travels at a constant speed along the existing line, and its horizontal position changes linearly with time, which is the position where the train load is applied. for:

[0182] ;

[0183] in, For a moment Horizontal position coordinates of the train load

[0184] These are the initial position coordinates of the train;

[0185] In actual train operation, due to factors such as track irregularities and wheel wear, the dynamic load will be greater than the static load, necessitating the introduction of a dynamic load factor. After correction, the actual dynamic load acting on the roadbed surface is obtained, specifically:

[0186] ;

[0187] in, The corrected transient dynamic load for the train.

[0188] The dynamic load coefficient Determined based on existing railway operation conditions and on-site test data;

[0189] As a further preferred method, the specific operation for calculating the transient excitation force of the train is as follows: [The text abruptly ends here, likely due to an incomplete or corrupted source.] As a dynamic load boundary condition, it is applied to the surface of the existing railway subgrade in the numerical model, and the location of the load application changes with time. The train moves in a regular pattern to simulate the dynamic load process when it is moving at a constant speed.

[0190] Under the dynamic load of the train, the soil deformation and groundwater seepage will have a dynamic interaction. It is necessary to establish a fluid-structure dynamic coupling equation to combine the dynamic load, excavation unloading static force, and pore water pressure change for coupled solution, including displacement equilibrium equation and seepage continuity equation.

[0191] The displacement equilibrium equation is used to describe the dynamic equilibrium relationship of soil under the combined action of dynamic and static loads, taking into account the effects of inertial force and damping force, specifically:

[0192] ;

[0193] in, The soil mass matrix, calculated from parameters such as soil density and element volume, reflects the inertial properties of the soil.

[0194] Let be the soil acceleration vector.

[0195] This is the soil damping matrix, which reflects the energy dissipation during soil vibration.

[0196] Let be the soil velocity vector.

[0197] This is the soil stiffness matrix, reflecting the elastic deformation characteristics of the soil.

[0198] Let be the soil displacement vector.

[0199] This is the fluid-structure interaction matrix, reflecting the effect of pore water pressure on soil deformation.

[0200] The pore water pressure vector.

[0201] The train dynamic load vector is given by The conversion yields the result; This is a static load vector, including the soil's self-weight and the unloading stress from the foundation pit excavation. Static forces included;

[0202] The seepage continuity equation is used to describe the continuity of groundwater seepage under dynamic loads, considering the influence of soil deformation on seepage, specifically:

[0203] ;

[0204] in, The seepage stiffness matrix is ​​calculated from the soil permeability coefficient k.

[0205] The pore water pressure vector.

[0206] For water storage matrix,

[0207] Let be the vector of the rate of change of pore water pressure.

[0208] Fluid-structure interaction matrix The transpose of the matrix, with dimensions equal to... on the contrary,

[0209] Let be the soil velocity vector.

[0210] The seepage flow vector is the pumping rate from the dewatering well. Sure.

[0211] During operation, the dynamic coupling solution module of the numerical simulation software is used to solve the displacement equilibrium equation and the seepage continuity equation simultaneously, and the pore water pressure field at the current construction stage is substituted into the equation. Effective stress state of soil and train dynamic load A fluid-structure interaction iterative solution is performed to obtain the total effective stress tensor of the strata at each location at each time step. .

[0212] The additional stress field refers to the extra stress generated in the strata under the combined effects of foundation pit excavation unloading, changes in dewatering water pressure, and the dynamic and static loads of trains. Specifically, it is the difference between the current stress state and the initial stress state.

[0213] ;

[0214] For a moment ,coordinate The effective additional stress tensor at the location,

[0215] For three-dimensional coordinates in space, For burial depth,

[0216] At the initial moment, the effective stress tensor of the soil at this location is calculated from the initial geostress field, specifically as follows:

[0217] ;

[0218] The initial total vertical stress,

[0219] The initial pore water pressure;

[0220] Extract each construction step and each spatial location from the numerical model. The distribution of the additional stress field of the stratum under the combined action of dynamic and static loads is obtained, providing stress input parameters for subsequent calculation of soil compression deformation.

[0221] In step S400, during the dewatering process of the foundation pit, the pore water pressure dissipates and the effective stress of the soil increases, which will lead to consolidation compression of the soil. The amount of consolidation compression is the main component of the roadbed settlement and is one-dimensional consolidation compression.

[0222] The one-dimensional consolidation compression calculation first assumes that the soil compresses only in the vertical direction. The strata are divided into soil layers, and the compression of each layer is calculated. The total consolidation compression is then obtained by summing the results. Specifically:

[0223] ;

[0224] This represents the total consolidation compression of the soil.

[0225] The average effective additional stress of the i-th soil layer is given by the additional stress field. The average stress value of this layer is obtained.

[0226] Let be the compression modulus of the i-th soil layer.

[0227] Let be the thickness of the i-th soil layer.

[0228] In another embodiment of the present invention, the consolidation compression can also be three-dimensional consolidation compression. The calculation considers the compression deformation of the soil in three-dimensional space, and the consolidation compression is calculated from volumetric strain. Specifically:

[0229] ;

[0230] in, This represents the volumetric strain of the soil, i.e., the rate of volume change caused by three-dimensional compressive deformation.

[0231] The average effective additional stress of the soil is determined by... Calculations show that

[0232] The soil's triaxial compression modulus and elastic modulus are given. Poisson's ratio Related, the conversion formula is as follows .

[0233] Because the excavation and unloading of the foundation pit will disrupt the original stress balance of the soil, causing lateral and vertical displacements in the surrounding soil, these displacements need to be directly extracted using a numerical model to obtain the time-varying displacements. ,coordinate At the location, the soil displacement vector caused by the unloading of the foundation pit is as follows:

[0234] ;

[0235] The soil displacement vector includes vertical displacement. and horizontal displacement , ;

[0236] In the numerical model, the train dynamic load and the effect of precipitation are turned off, and only the unloading process of the foundation pit excavation is simulated to obtain the pure unloading displacement field. The vertical and lateral displacement components at each location are extracted for subsequent total displacement superposition.

[0237] The total dynamic displacement of the soil is the superposition of consolidation compression displacement and foundation pit unloading displacement, including both vertical settlement and lateral displacement. The result after superposition is:

[0238] ;

[0239] In the formula: This represents the total dynamic displacement vector of the soil.

[0240] Let be the soil consolidation compression displacement vector, derived from the consolidation compression amount. The transformation yields,

[0241] The soil displacement vector caused by unloading of the foundation pit is equal to .

[0242] The specific operation is as follows: the consolidation compression displacement vector and the unloading displacement vector at each construction step and each location are vector-superimposed to obtain the total dynamic displacement. The focus is on extracting the vertical displacement component, while also recording the lateral displacement component, to analyze the causes of uneven deformation of the roadbed.

[0243] After superimposing the consolidation compression displacement and the foundation pit unloading displacement, dynamic deformation and displacement data of each location of the adjacent composite foundation and underlying soil layer are obtained under each excavation and dewatering stage, including vertical settlement increment, lateral displacement, and displacement change curve over time.

[0244] In step S500, the cumulative settlement of the existing roadbed is the sum of the settlement increments of the roadbed at each construction step throughout the entire excavation and dewatering cycle, that is, the sum of the vertical components of the total dynamic displacement of the soil at each construction step, specifically:

[0245] ;

[0246] in, Coordinates of the existing line base surface The cumulative settlement at the location,

[0247] For the k-th construction step, the coordinates are... The subgrade settlement increment at point k is the total dynamic displacement of the soil at the k-th construction step. The vertical component.

[0248] Uneven deformation is used to reflect the difference in roadbed settlement, which directly affects the safety of train operation on existing lines, including the maximum uneven settlement and the roadbed inclination.

[0249] The maximum uneven settlement is the difference between the maximum and minimum cumulative settlement within the calculated section of the roadbed, specifically:

[0250] ;

[0251] in, This represents the maximum uneven settlement of the roadbed.

[0252] This represents the maximum cumulative settlement within the calculated section of the roadbed, i.e. The maximum value in,

[0253] This is the minimum cumulative settlement within the roadbed calculation section, i.e. The minimum value in.

[0254] The slope of the roadbed This is the ratio of the uneven settlement difference within the calculated section of the roadbed to the length of the calculated section, reflecting the degree of tilt in the roadbed settlement. Specifically:

[0255] ;

[0256] in, The length of the roadbed calculation section is determined based on the existing track span and roadbed width.

[0257] The roadbed settlement prediction curves include time-settlement curves, spatial settlement cloud maps, and depth-settlement curves to intuitively reflect the temporal and spatial variation patterns of existing roadbed settlement.

[0258] The time-settlement curve is used to characterize the variation of the cumulative settlement of the roadbed at a specific location with the construction time.

[0259] The spatial settlement cloud map is used to characterize the spatial distribution of the cumulative settlement on the surface of the existing railway subgrade at a certain construction time.

[0260] The depth-settlement curve is used to characterize the distribution pattern of cumulative settlement at different depths of the existing railway subgrade and underlying layer.

[0261] When generating the subgrade settlement prediction curve, data processing software is used to fit and interpolate the summarized settlement data to generate the above three types of settlement prediction curves, which clearly present the temporal and spatial variation characteristics of subgrade settlement.

[0262] Then, all calculation results are summarized, and four core quantitative indicators are extracted as the final output for the prediction of existing railway subgrade settlement. These indicators are used for the safety assessment and construction control of existing railway lines. The specific indicators include:

[0263] Maximum cumulative settlement Maximum uneven settlement Maximum inclination and settling rate ;

[0264] The settling rate The derivative is obtained from the settlement time curve. This reflects the rate of subgrade settlement development; when the settlement rate approaches 0, the subgrade settlement reaches a stable state.

[0265] Finally, the above four quantitative indicators were compiled into a booklet and combined with the settlement prediction curve to form the final settlement prediction report for the existing line subgrade, providing accurate quantitative basis for the safety control and construction parameter adjustment of the existing line during the foundation pit construction process.

[0266] Example 2

[0267] This invention provides a system for predicting the settlement of existing railway subgrade during foundation pit excavation based on water pressure, comprising:

[0268] Data acquisition module: used to acquire geological survey data of the construction area, design parameters for foundation pit dewatering and existing railway structure parameters, construct a three-dimensional fluid-structure coupling numerical model including foundation pit, composite foundation and existing line, and set boundary conditions for soil constitutive relation, initial pore water pressure field and initial ground stress field of strata;

[0269] Data simulation module: It is used to simultaneously simulate the groundwater pumping and soil excavation unloading process in the numerical model according to the foundation pit dewatering plan and the layered excavation sequence. It uses the seepage control equation to calculate in real time the dissipation process, dynamic distribution of pore water pressure inside and outside the foundation pit under different construction stages, as well as the spatial drop surface of the groundwater level.

[0270] Coupled solution module: used to establish the transient excitation force function of existing line train operation to characterize the real dynamic load, apply it to the roadbed surface, and perform fluid-structure dynamic coupling solution with the updated pore water pressure field and soil effective stress state of the current construction stage to calculate the additional stress field of the stratum under the combined action of dynamic and static loads.

[0271] Displacement calculation module: used to extract additional stress and pore water pressure dissipation, calculate the consolidation compression of the soil around the foundation pit due to the increase in effective stress, and superimpose the lateral and vertical displacement of the soil caused by the unloading of the foundation pit to obtain the dynamic deformation and displacement data of the adjacent composite foundation and underlying soil under each excavation and dewatering stage.

[0272] Prediction output module: used to summarize soil compression and deformation displacement data at different depths, calculate and extract the cumulative settlement and uneven deformation of existing railway subgrade during the entire excavation and dewatering cycle, generate settlement prediction curves of existing subgrade that vary with time and space, and output the final quantitative indicators of settlement prediction.

[0273] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure, characterized in that, Specifically, the following steps are included: S100. Construct a three-dimensional fluid-structure interaction numerical model and set the boundary conditions for soil constitutive relations, initial pore water pressure field and initial geostress field of strata. S200. Simultaneously simulate the groundwater pumping and soil excavation unloading process in the numerical model. Utilize the seepage control equation to calculate in real time the dissipation process, dynamic distribution, and spatial drop surface of the groundwater level inside and outside the foundation pit under different construction stages. S300. Establish the transient excitation force function of existing line train operation to characterize the real dynamic load, and perform fluid-structure dynamic coupling solution with the updated pore water pressure field and soil effective stress state in the current construction stage to calculate the additional stress field of the stratum under the combined action of dynamic and static loads. S400, extract additional stress and pore water pressure dissipation, calculate the consolidation compression of the soil around the foundation pit due to the increase in effective stress, and superimpose the dynamic deformation and displacement data of the adjacent composite foundation and underlying soil at each excavation and dewatering stage. S500: Calculate and extract the cumulative settlement and uneven deformation of the existing railway subgrade during the entire excavation and dewatering cycle, generate the settlement prediction curve of the existing subgrade that varies with time and space, and output the final quantitative index of settlement prediction. Under the dynamic load of the train, the soil deformation and groundwater seepage will have a dynamic interaction. It is necessary to establish a fluid-structure dynamic coupling equation to combine the dynamic load, excavation unloading static force, and pore water pressure change for coupled solution, including displacement equilibrium equation and seepage continuity equation. The displacement equilibrium equation is used to describe the dynamic equilibrium relationship of soil under the combined action of dynamic and static loads, taking into account the effects of inertial force and damping force, specifically: in, The soil mass matrix, calculated from soil density and element volume, reflects the inertial properties of the soil. Let be the soil acceleration vector. This is the soil damping matrix, which reflects the energy dissipation during soil vibration. Let be the soil velocity vector. This is the soil stiffness matrix, reflecting the elastic deformation characteristics of the soil. Let be the soil displacement vector. This is the fluid-structure interaction matrix, reflecting the effect of pore water pressure on soil deformation. The pore water pressure vector. The train dynamic load vector is given by The conversion yields the result; This is a static load vector, including the soil's self-weight and the unloading stress from the foundation pit excavation. Static forces included; The seepage continuity equation is used to describe the continuity of groundwater seepage under dynamic loads, considering the influence of soil deformation on seepage, specifically: in, The seepage stiffness matrix is ​​calculated from the soil permeability coefficient k. The pore water pressure vector. For water storage matrix, Let be the vector of the rate of change of pore water pressure. Fluid-structure interaction matrix The transpose of the matrix, with dimensions equal to... on the contrary, Let be the soil velocity vector. The seepage flow vector is the pumping rate from the dewatering well. Sure.

2. The method for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure, as described in claim 1, is characterized in that... In the three-dimensional fluid-structure interaction numerical model, for saturated soil, the mutual influence between groundwater seepage and soil deformation during the excavation of the foundation pit is considered. The small deformation and quasi-static assumptions are adopted to establish the three-dimensional fluid-structure interaction control equations, including the equilibrium equation, the effective stress principle and the seepage continuity equation.

3. The method for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure, as described in claim 2, is characterized in that... The equilibrium equations are used to describe the static equilibrium relationship of soil under stress, that is, the spatial variation of total stress within the soil is balanced with the volume forces, specifically: in, The Hamiltonian operator represents the spatial derivative operation. The total stress tensor of the soil reflects the total force acting on a unit area of ​​the soil. This is a volume force vector, including the soil's self-weight, with the vertically downward direction being positive. The principle of effective stress is as follows: During the excavation and dewatering of the foundation pit, the soil is subjected to two forces: effective stress and pore water pressure. Effective stress is the key factor determining soil deformation and strength, and the relationship between the two is as follows: in, This is the effective stress tensor of the soil, which is the stress that actually acts on the contact surface of soil particles after deducting pore water pressure from the total stress. This refers to pore water pressure, which is the pressure exerted on the water within the pores of the soil. It is a unit tensor, used to ensure dimensionality consistency in tensor operations; The seepage continuity equation is used to describe the continuity of groundwater seepage during the dewatering process of foundation pits. Specifically, the difference between the amount of water flowing into and out of a soil unit per unit time is equal to the change in pore water volume within that unit. in, The soil permeability tensor reflects the soil's ability to allow groundwater to seep through; different soil layers have different permeability coefficients. For the Laplace operator, The density of water, This represents the volumetric strain of the soil, which is the ratio of the change in soil volume to the initial volume. This refers to the construction period.

4. The method for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure, as described in claim 3, is characterized in that... The boundary conditions include displacement boundaries and seepage boundaries; The displacement boundaries are as follows: the bottom of the model is subject to fixed constraints to prevent unreasonable settlement or heave of the bottom soil; the sides of the model are subject to normal constraints to simulate the constraint effect of infinitely extended strata in actual engineering, which is achieved by setting numerical model parameters. The seepage boundary is defined as follows: the natural ground surface is the permeable boundary, the initial groundwater level is the constant head boundary, the dewatering well is the constant flow or constant drawdown boundary, and the sides and bottom of the model are the impermeable boundaries.

5. A method for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure, as described in any one of claims 1-4, characterized in that... In step S200, when calculating the external pore water pressure in the foundation pit, the finite element method is used to iteratively solve the seepage continuity equation in real time, taking into account the excavation unloading and dewatering conditions of each construction step. This allows for the real-time calculation of the dissipation process, dynamic distribution, and groundwater level drop surface of the pore water pressure inside and outside the foundation pit at different construction stages. The finite element iteration formula is as follows: in, This is a permeability matrix, reflecting the influence of soil permeability characteristics on seepage. For a moment The pore water pressure vector The seepage boundary load vector is determined by the seepage boundary conditions. For water storage matrix, Let be the pore water pressure vector at time t. The time step is consistent with the time interval of the discretization of the construction steps; In practice, the above formula is embedded into the model, and transient seepage iterations are performed for each construction step to output the pore water pressure values ​​at different locations inside and outside the foundation pit at each moment. Then, pore water pressure cloud maps and groundwater level drop contour surfaces are plotted, and the dissipation rate of excess pore water pressure is calculated. The dynamic variation of pore water pressure with construction time and spatial location was clarified.

6. A method for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure, as described in any one of claims 1-4, characterized in that... In step S300, since the train's wheels generate transient dynamic loads when in contact with the track, and these loads vary with time and space, they need to be simplified into a sequence of moving concentrated loads. A transient excitation force function is then established to characterize the magnitude, frequency, and movement characteristics of the actual dynamic load. When establishing the transient excitation force function, the train load is simplified to a moving concentrated load, and the magnitude of its transient excitation force is related to the train's axle load and speed, specifically: in, Let be the transient excitation force of the train at time t. This is the static load on a single axle of the train, determined by the axle load of the train, and equal to the axle load value. Let be the influence function of dynamic load. The dynamic load influence function Used to characterize the influence of train speed and position on the excitation force, its value is related to the train speed. and the position of train load Related.

7. The method for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure, as described in claim 6, is characterized in that... The train travels at a constant speed along the existing line, and its horizontal position changes linearly with time, which is the position where the train load is applied. for: in, For a moment Horizontal position coordinates of the train load These are the initial position coordinates of the train; During actual train operation, due to factors such as track irregularities and wheel wear, the dynamic load will be greater than the static load, necessitating the introduction of a dynamic load factor. After correction, the actual dynamic load acting on the roadbed surface is obtained, specifically: in, The corrected transient dynamic load for the train. The dynamic load coefficient It is determined based on the existing railway operation and on-site test data.

8. A method for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure, as described in any one of claims 1-4, characterized in that... In step S500, the roadbed settlement prediction curve includes a time-settlement curve, a spatial settlement cloud map, and a depth-settlement curve; When generating the subgrade settlement prediction curve, data processing software is used to fit and interpolate the summarized settlement data to generate the above three types of settlement prediction curves. Then, all calculation results are summarized, and four core quantitative indicators are extracted as the final output for the settlement prediction of existing railway subgrade. These indicators include: maximum cumulative settlement. Maximum uneven settlement Maximum inclination and settling rate ; The settling rate The settlement-time curve is derived to reflect the rate of subgrade settlement. When the settlement rate approaches 0, the subgrade settlement reaches a stable state.

9. A system for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure, used to implement the method for predicting settlement of existing railway subgrade during foundation pit excavation based on water pressure as described in any one of claims 1-8, characterized in that, include: Data acquisition module: used to construct a three-dimensional fluid-structure interaction numerical model and set the boundary conditions for soil constitutive relations, initial pore water pressure field and initial geostress field of strata; Data simulation module: used to simultaneously simulate the groundwater pumping and soil excavation unloading process in the numerical model, and to calculate in real time the dissipation process, dynamic distribution and spatial drop surface of pore water pressure inside and outside the foundation pit under different construction stages using the seepage control equation. Coupled solution module: used to establish the transient excitation force function of existing line train operation to characterize the real dynamic load, and perform fluid-structure dynamic coupling solution with the updated pore water pressure field and soil effective stress state of the current construction stage to calculate the additional stress field of the stratum under the combined action of dynamic and static loads. Displacement calculation module: used to extract additional stress and pore water pressure dissipation, calculate the consolidation compression of the soil around the foundation pit due to the increase in effective stress, and superimpose the dynamic deformation and displacement data of the adjacent composite foundation and underlying soil at each excavation and dewatering stage. Prediction output module: used to calculate and extract the cumulative settlement and uneven deformation of the existing railway subgrade during the entire excavation and dewatering cycle, generate the settlement prediction curve of the existing subgrade that varies with time and space, and output the final quantitative index of settlement prediction.

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