Three-surface integrated geologic structure modeling method for deep and large foundation pit in adjacent river region

Abstract

The invention belongs to the field of soil rock engineering, and provides a three-surface integrated geologic structure modeling method for a deep and large foundation pit in a river-adjacent region, which comprises the following steps: acquiring physical and mechanical parameters and hydrogeological information of the deep and large foundation pit in the river-adjacent region; dividing spatial distribution of different soil layers and rock stratums; describing the influence of water level time variation on the pore water pressure and subsurface erosion of the surrounding rock of the foundation pit through an unstable seepage equation; dividing a finite element or finite difference grid, and applying a dynamic water level and ground load boundary condition; gradually unloading and analyzing the evolution of an underground water flow field and a soil-rock deformation field in each excavation step, and enabling the water surface-ground-soil-rock surface coupling effect to penetrate through the whole excavation process; and numbering the support members, sequentially simulating local failures of the support members, recording the maximum horizontal displacement, the maximum vertical displacement or the change curve of the safety coefficient along with the number of the failure members after each failure of the foundation pit, quantifying the redundancy of the support system, and identifying key members. According to the scheme, the accuracy of the model is improved.

Description

Technical Field

[0001] The present invention belongs to the field of soil and rock engineering, and in particular relates to a three-sided integrated geological structure modeling method for a deep and large foundation pit in a Linjiang area. Background Art

[0002] In recent years, with the continuous expansion of urban construction, demand for underground space development in riverside areas has increased. Deep and large foundation pits are widely used in major projects such as rail transit, high-rise buildings, and underground complexes. These deep and large foundation pits in riverside areas generally face complex and changing hydrogeological conditions. These factors, particularly the dynamic fluctuations in the water levels of nearby rivers, the complexity of the soil-rock interface, and varying ground loads, make deformation control and stability analysis of foundation pits significantly challenging.

[0003] In riverside areas, such as the Sichuan Basin, deep and large foundation pits are often located in environments with dense surface loads, drastically changing hydrological conditions, and complex geological structures. Numerous engineering projects have shown that the stability of foundation pits in riverside areas is not only affected by surface loads (such as construction and traffic loads), but is also significantly constrained by frequent fluctuations in river water levels. Relevant hydrological monitoring data shows that river water levels in the Sichuan Basin exhibit the typical characteristics of "rapid rise and slow decline" during flood seasons. This means that water levels typically rise for 13 days, while the water level decline period can last up to 37 days. This change directly leads to an increase in the unstable seepage effect of the groundwater level, inducing sudden stress changes in the foundation pit support structure and seepage damage to the surrounding rock.

[0004] Furthermore, the widespread distribution of soil-rock transitional strata in riverside areas further exacerbates the uncertainty surrounding foundation pit stability. Traditional geological modeling methods often treat soil and rock strata separately, failing to accurately reflect the damage evolution of the soil-rock interface under hydraulic pressure and construction disturbances, making it difficult to predict the true development trend of foundation pit deformation. In actual projects, the erosion zone formed by the seepage of river water and the scouring of fine particles at the soil-rock interface makes the soil-rock interface a control surface for sliding failure. Local failure of the support structure can rapidly trigger overall instability, resulting in serious engineering accidents.

[0005] The existing technology still lacks a geological structure modeling method that can fully integrate the coupling effects of the water surface, ground surface, and soil-rock surface, and consider the dynamic changes in hydrology and the damage mechanism of the soil-rock interface. At the same time, the assessment methods of the overall stability of the support structure mostly rely on a single safety factor, do not fully quantify the system redundancy under local failure conditions, and do not introduce intelligent algorithms to quickly and accurately predict the stability of the support system. Therefore, it is urgent to propose a "three-in-one" geological structure modeling method suitable for deep and large foundation pits near the river, combining redundancy theory with intelligent evaluation algorithms to achieve systematic analysis and scientific evaluation of the stability of foundation pit support systems in complex environments, so as to ensure project safety and controllable construction. Summary of the Invention

[0006] In order to solve the problems in the prior art, the present invention provides a three-dimensional geological structure modeling method for a deep and large foundation pit in Linjiang area, comprising the following steps: Obtain the physical and mechanical parameters and hydrogeological information of the deep excavation area in Linjiang River, collect data on the changes in Linjiang River water levels over the years and the water levels of groundwater observation wells, and combine ground loads with environmental information to generate data for a three-dimensional coupled analysis of the water surface, ground surface, and soil and rock surface. Based on the drilling and testing results, the spatial distribution of different soil and rock layers is divided, and the weak interlayers, fracture development zones or potential damage zones at the soil-rock interface are identified. The soil-rock interface is described using contact elements or weakened zone models. The change process of the Linjiang River water level from abrupt rise to temporary stability to slow drop is transformed into a time-varying seepage boundary condition. The influence of the time-varying water level on the pore water pressure and erosion of the foundation pit surrounding rock is described by the unsteady seepage equation. Based on the three-dimensional spatial characteristics of the surface topography and underlying rock and soil layers, a finite element or finite difference grid is created to characterize the mechanical and seepage properties of the soil, rock, and soil-rock interface, and dynamic water level and ground load boundary conditions are applied. According to the actual excavation sequence of the foundation pit and the support structure layout plan, the groundwater flow field and the evolution of the soil and rock deformation field in each excavation step are gradually unloaded and analyzed, and the coupling effect of the water surface, ground surface and soil and rock surface is integrated throughout the excavation process; The support components are numbered and their local failures are simulated in sequence. The maximum horizontal displacement, maximum vertical displacement or safety factor of the foundation pit after each failure is recorded as a function of the number of failed components. The redundancy of the support system is quantified and key components are identified.

[0007] Furthermore, the physical and mechanical parameters include the natural density, porosity, saturation, permeability, cohesion, internal friction angle and elastic modulus of each stratum.

[0008] Furthermore, the hydrogeological information includes data on changes in the water level of the adjacent river over the years and time series data on the water level recorded in groundwater observation wells around the foundation pit.

[0009] Furthermore, the weak zone model reflects the weakness and damage characteristics of the soil-rock interface by adjusting the interface strength parameter or stiffness parameter.

[0010] Furthermore, the finite difference grid satisfies the following conditions: a) The grid density and cell size are adaptively set according to the stratum gradient, and a fine grid is used in the soil-rock interface area to improve local accuracy; b) The soil layer elements adopt tetrahedron or hexahedron elements suitable for porous media seepage and constitutive models. The rock mass elements consider the influence of cracks and introduce nested crack elements. c) Contact elements or weakening elements are set at the soil-rock interface to realize the friction, slip and hydraulic coupling behaviors of the interfaces between different materials.

[0011] Furthermore, the load boundary conditions meet the following conditions: a) Apply a constant head boundary condition to the riverside boundary to simulate the effect of river water seepage into the surrounding rock system; b) Set drainage conditions or constant flow boundaries at the bottom of the foundation pit and the far-field boundary to maintain hydraulic balance inside and outside the model; c) During the water level rise, the boundary head increases at the rate of the steep rise stage, remains unchanged during the time-stable period, and decreases linearly during the slow drop period.

[0012] Furthermore, after dividing the finite element or finite difference grid that can characterize the mechanical and seepage characteristics of the soil, rock mass, and soil-rock interface, and applying the dynamic water level and ground load boundary conditions: The stability of the preliminary grid division and boundary condition setting is verified, and grid independence analysis is used to ensure that the influence of unit density on the calculation results is controllable. Local encryption is performed around the support structure and at the soil-rock interface.

[0013] Furthermore, after each excavation step, the construction and activation of the corresponding support components are simulated according to the support structure layout plan, including: Simulate support pile placement and apply stiffness and boundary constraints; Install anchor rods and apply prestressing force; Add sprayed anchors and internal support systems to apply constrained displacement or reaction force.

[0014] Furthermore, in each excavation step, comprehensive consideration should be given to: Seepage field and pore water pressure changes caused by water surface changes, The influence of ground load on the stress field of surrounding rock, Stress concentration and erosion evolution at soil-rock interface under seepage-deformation action.

[0015] Furthermore, after quantifying the redundancy of the support system and identifying key components, the redundancy change curve, key component numbers and their corresponding positions are output to determine the redundancy capacity limit of the support system, optimize component layout and parameter configuration, conduct construction quality control and real-time monitoring of key components, and form emergency reinforcement and risk management plans for local failures to ensure the safety and stability of the entire foundation pit construction process.

[0016] This paper provides a "three-in-one" geological structure modeling and foundation pit support system stability evaluation method for deep and large foundation pits in the Linjiang area. Based on an in-depth analysis of the complex hydrogeological environment in the Linjiang area, it has the following beneficial effects: Based on the changing characteristics of the adjacent river water level, which is "steep rise-temporal stability-slow drop", this method constructs dynamic seepage boundary conditions and solves the groundwater flow field through the unsteady seepage equation. It can accurately simulate the spatiotemporal impact of water level changes on the pore water pressure distribution and the erosion behavior of the soil-rock interface, thereby effectively guiding the support design and construction schedule under complex hydrological conditions.

[0017] By adopting a "three-in-one" geological structure model, we systematically integrate the water surface water level load, ground construction load and soil-rock interface damage characteristics to construct a high-precision three-dimensional model that truly reflects the surrounding rock response of the deep and large foundation pit near the river. This model comprehensively reveals the deformation and instability mechanism of the foundation pit under the action of hydraulic-mechanical coupling, and improves the accuracy of model prediction.

[0018] By simulating the failure of support components in sequence and recording the changes in key deformation parameters and safety factors of the foundation pit, the redundancy of the support system is quantitatively calculated, key components are identified, and the impact of local damage on overall stability is comprehensively evaluated. This provides data support for optimizing support structure configuration and emergency response, and enhances the project's risk resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0021] Below, the invention is preferably described with reference to the accompanying drawings and specific embodiments.

[0022] This embodiment solves the above problem through the following steps: In one embodiment, reference Figure 1 The present invention provides a three-faceted geological structure modeling method for deep and large foundation pits in Linjiang area. On the basis of fully considering the complex hydrogeological environment of Linjiang area, the dynamic change characteristics of Linjiang water level, the surface load of the site and the geological structure characteristics are comprehensively considered to establish a unified geological structure model covering the triple interfaces of water surface, ground surface and soil-rock surface. Through multi-source data fusion, seepage-mechanical coupling analysis and step-by-step excavation simulation, the deformation evolution and instability mechanism of the deep and large foundation pit in Linjiang under the coordinated action of water level changes, soil-rock interface damage and support system are fully reflected, thereby providing a scientific basis for foundation pit design, construction and safety control.

[0023] Specifically, the method comprises the following steps: Step S10, obtain the physical and mechanical parameters of the deep foundation pit area near the river, collect the water level changes of the river and the water level data of the groundwater observation wells over the years, combine the ground load and environmental information, and form the data of the three-surface coupling analysis of water surface, ground surface and soil and rock surface.

[0024] In the present invention, the deep and large foundation pit area near the river refers to the foundation pit engineering area with a large excavation depth and a wide plane range set up near natural river channels (such as the Minjiang River, Jialing River, etc.), which often involves complex hydrogeological conditions, soil-rock interaction structure, and high water level seepage characteristics.

[0025] The physical and mechanical parameters and hydrogeological information of the rock and soil in the area where the deep and large foundation pit project in Linjiang area is located are obtained. The physical and mechanical parameters of the rock and soil include but are not limited to the natural density, porosity, saturation, permeability, cohesion, internal friction angle and elastic modulus of each stratum. The hydrogeological information includes the water level change data of Linjiang over the years and the water level time series data recorded in the groundwater observation wells around the foundation pit. The ground load information and environmental change data of the foundation pit site and surrounding areas are further obtained. The ground load information includes the upper building load, traffic load, construction load and mechanical load. The environmental change data includes environmental factors such as rainfall, wind, and temperature. Based on the above-obtained data, a comprehensive coupling relationship between the water surface boundary, ground load boundary and soil-rock interface structure in the deep and large foundation pit area of ​​Linjiang is established to form a basic data set for the subsequent water surface-ground-soil-rock interface coupling analysis, providing data support for the subsequent geological structure model construction and foundation pit stability analysis.

[0026] Step S20 divides the spatial distribution of different soil and rock layers based on the drilling and testing results, identifies weak interlayers, fracture development zones or potential damage zones at the soil-rock interface, and describes the soil-rock interface using contact units or a weakened zone model.

[0027] Based on the drilling exploration data and geotechnical test results of the Linjiang Deep Foundation Pit Project area, the distribution range and geometric form of different soil and rock layers in three-dimensional space are divided. The drilling exploration data include core description, stratum thickness, burial depth and inclination information. The geotechnical test results include physical and mechanical parameters and permeability characteristics of each layer. After the division is completed, the soil-rock interface at the contact point between the soil layer and the rock layer is identified, and further analysis is performed on whether there are weak interlayers, fracture development zones or potential damage zones formed by long-term hydraulic action in the interface. The weak interlayer is a thinner and lower-strength mud or silt interlayer, and the fracture development zone is a rock mass with dense cracks and a penetrating The potential damage zone is an area with strong connectivity, and the potential damage zone is a structural area weakened by hydraulic or load effects. After identification is completed, the soil-rock interface is described in the geological structure model using a contact unit or a weakened zone model. The contact unit is used to simulate the friction, slip and separation behavior between the soil layer and the rock layer. The weakened zone model reflects the weakness and damage characteristics of the soil-rock interface by adjusting the interface strength parameter or stiffness parameter. Through the above modeling method, the geological model's ability to characterize the actual geological structure and mechanical behavior of the deep and large foundation pit area near the river is improved, providing a real and accurate basic model support for subsequent seepage analysis, deformation analysis and stability assessment.

[0028] Step S30 converts the change process of the adjacent river water level from abrupt rise to temporary stability to a slow drop into a time-varying seepage boundary condition, and describes the influence of the time-varying water level on the pore water pressure and erosion of the foundation pit surrounding rock through the unsteady seepage equation.

[0029] The characteristic water level evolution process of abrupt rise, temporary stability, and gradual decline is common in the hydrological changes of neighboring rivers. This process involves a rapid rise in the river (abrupt rise), followed by a period of sustained high water levels (temporal stability), and finally a gradual decline over a longer period (a gradual decline). This process exhibits significant temporal and phased characteristics, significantly impacting the groundwater flow field and the stability of the surrounding rock mass of foundation pits.

[0030] Based on the flood observation data of the adjacent river over the years and the hydrological response law of the adjacent river area, a mathematical model of water level change over time is constructed. The water level function is set as , which is defined as follows: ,

[0031] in: is the initial water level (m), is the peak water level (m), is the water level rising rate (m / s), is the water level drop rate (m / s), For the time node.

[0032] The water level function Applied to the boundary of the river side in the geological structure model to define the boundary head at this boundary , and set its time-varying characteristics to form a time-varying seepage boundary.

[0033] In the model, the unsteady seepage equation in the control area is solved based on the permeability parameter k and the water storage coefficient s: , The solution goal is to determine any time t and space point Head distribution under , and the pore water pressure is calculated from this ,in: , is the unit weight of water (kN / m³).

[0034] By calculating the pore water pressure gradient , judge the area where erosion occurs, and erosion is considered to have started when the following formula is met: , in, is the corrosion initiation threshold (kPa / m), which can be determined by field tests or empirical values.

[0035] For areas that meet the erosion conditions, adjust the permeability coefficient k and the strength parameter c, , so that it changes with the development of erosion, and the update formula is as follows: , ,

[0036] in: β is the permeability enhancement coefficient, δ is the strength degradation coefficient, Δt is the time increment.

[0037] The above calculations are iteratively performed in the time domain to obtain the dynamic distribution of the pore water pressure field and the area affected by erosion and scouring throughout the excavation process, ultimately providing complete seepage and water pressure input conditions for foundation pit stability analysis and support design.

[0038] In this step, by converting the evolution process of the adjacent river water level into a time-varying seepage boundary condition in the form of a mathematical function, and combining it with the unsteady seepage theory and erosion simulation, it can not only truly reflect the impact of the adjacent river water level on groundwater flow and the pore water pressure of the foundation pit surrounding rock, but also accurately simulate the seepage damage evolution process at the soil-rock interface and around the foundation pit, thereby improving the accuracy and reliability of the geological structure model and providing scientific support for the subsequent support structure safety assessment and instability mechanism analysis.

[0039] Step S40 divides the finite element or finite difference grid that can characterize the mechanical and seepage characteristics of the soil, rock and soil-rock interface based on the three-dimensional spatial characteristics of the surface topography and underlying rock and soil layers, and applies dynamic water level and ground load boundary conditions.

[0040] The three-dimensional spatial characteristics of the underlying rock and soil layers refer to the distribution patterns of the soil and rock layers in the foundation pit area in three-dimensional space, including layer thickness, interlayer interface fluctuations, rock property changes, and soil-rock interface morphology. They are the core basis for constructing a real geological structure model.

[0041] In this step, a surface digital elevation model (DEM) is constructed based on the drilling data, geological profile, and topographic mapping data obtained in step S20 to form the surface geometric boundary of the foundation pit area; based on the spatial distribution information of the soil and rock layers, the inverse distance weighted method (IDW) or Kriging interpolation method is used to fit the interfaces of each layer to reconstruct the three-dimensional spatial structure model of the rock and soil layers.

[0042] Based on the three-dimensional geological model, the finite element method or finite difference method is used to discretize the surrounding rock area of ​​the foundation pit and divide it into unit grids with mechanical and seepage calculation capabilities. The grids meet the following conditions: a) The grid density and cell size are adaptively set according to the stratum gradient, and a fine grid is used in the soil-rock interface area to improve local accuracy; b) The soil layer elements adopt tetrahedron or hexahedron elements suitable for porous media seepage and constitutive models. The rock mass elements consider the influence of cracks and introduce nested crack elements when necessary. c) Contact elements or weakening elements are set at the soil-rock interface to realize the friction, slip and hydraulic coupling behaviors of the interfaces between different materials.

[0043] The water level function constructed according to step S30 , which is converted into a time-dependent boundary head function , applied to the boundary nodes on the river side of the geological model; the water level boundary meets the following conditions: a) Apply a constant head boundary condition to the riverside boundary to simulate the effect of river water seepage into the surrounding rock system; b) Set drainage conditions or constant flow boundaries at the bottom of the foundation pit and the far-field boundary to maintain hydraulic balance inside and outside the model; c) During the rising water level, the boundary head increases at the rate of the steep rise phase, remains unchanged during the steady phase, and decreases linearly during the slow fall phase, satisfying the following relationship: ,

[0044] in, Represents the boundary region where the hydraulic head is applied.

[0045] Based on the ground load data, static and dynamic loads such as buildings, traffic, and pile loads are mapped to the surface boundary nodes and vertical loads are applied. and horizontal loads ,in: ,

[0046] in, represents the boundary area where the ground load is applied, represents the normal stress, represents the tangential stress.

[0047] At the same time, free boundary conditions are set for other unloaded areas of the surface boundary, and rigid constraints or far-field constraints are set at the bottom of the model to ensure calculation stability and boundary effect control.

[0048] Furthermore, the stability of the initial meshing and boundary condition settings was verified. Mesh independence analysis was used to ensure that the impact of element density on the calculation results was controllable. Where necessary, local densification was performed in key areas (such as around support structures and at the soil-rock interface). Trial calculations were performed to verify the rationality of the model's stress and seepage field distribution under boundary loading, ensuring the accuracy of subsequent simulations.

[0049] The three-dimensional mesh discretization and dynamic boundary loading achieved in this step not only truly restore the complex geological environment of the Linjiang Deep Foundation Pit Project, but also accurately simulate the hydraulic-mechanical coupling effect, especially the response characteristics of the soil-rock interface and the accurate characterization of the ground load transfer path, providing a high-precision calculation model foundation for subsequent construction simulation, support analysis and stability evaluation. Step S50 gradually unloads and analyzes the evolution of groundwater flow field and soil-rock deformation field in each excavation step according to the actual excavation sequence of the foundation pit and the support structure layout plan, and integrates the three-surface coupling effect of water surface, ground surface and soil-rock surface throughout the entire excavation process.

[0050] According to the construction design documents, set the total depth of the foundation pit And the number of excavation layers N, the foundation pit excavation is divided into N excavation steps, and the excavation depth of each step is: , in: represents the excavation depth of step i (m), is the total designed excavation depth of the foundation pit (m), is the total number of excavation steps.

[0051] In the numerical model, the gravity load and additional load of each excavation area are gradually removed to update the stress field. and strain field , realizing the gradual unloading response of soil and rock mass.

[0052] After each excavation step, the construction and activation of the corresponding support components are simulated according to the support structure layout plan, including: Simulate support pile placement and apply stiffness and boundary constraints; Install anchor rods and apply prestressing ; Add support systems such as sprayed anchors and internal supports to apply constrained displacement or reaction force.

[0053] The supporting components enter the stress state after excavation, forming a counter-support effect on the surrounding rock of the foundation pit. Participate in foundation pit balance calculations.

[0054] After each excavation step, the time-varying water level boundary set in step S30 is , update the seepage boundary conditions based on the unsteady seepage equation: ,

[0055] Solve the head distribution of groundwater around the foundation pit , and calculate the pore water pressure .

[0056] in, represents the permeability coefficient (m / s); is the water storage coefficient (dimensionless), Indicates time (s) ,in is the unit weight of water (kN / m³).

[0057] After obtaining the updated pore water pressure Finally, the stress-strain response of the surrounding rock of the foundation pit is solved by combining the support structure effect and load changes to satisfy the equilibrium equation: ,

[0058] in: represents the stress tensor (kPa); Indicates the density of rock and soil (kg / m³); Represents the gravitational acceleration vector (m / s²).

[0059] And combined with the constitutive relationship: ,

[0060] Output foundation pit horizontal displacement , vertical displacement , shear stress and plastic zone distribution and other indicators; in, represents the constitutive matrix, represents the total strain; represents the plastic strain.

[0061] In each excavation step, comprehensive consideration should be given to: Water surface changes The changes in seepage field and pore water pressure caused by Ground load The impact on the surrounding rock stress field, Stress concentration and erosion evolution of soil-rock interface under seepage-deformation action, Achieve continuous simulation of the synergistic effects of water surface, ground surface and soil-rock surface, and update material parameters in real time in the model (such as the soil-rock interface caused by erosion). ), dynamically correct the seepage and mechanical responses to ensure that the model reflects the foundation pit response behavior under the actual construction environment.

[0062] Complete the simulation of all N steps of excavation and support processes and output key response indicators for each step, including: spatiotemporal distribution of groundwater head and pore water pressure; Maximum horizontal displacement of foundation pit , maximum vertical displacement ; Changes in internal forces of the supporting structure ; Extension of the plastic zone at the soil-rock interface and evolution of the erosion risk zone.

[0063] The above results serve as the basis for subsequent stability evaluation and optimization design.

[0064] Through the gradual unloading and dynamic response simulation in step S50, not only can the seepage and deformation characteristics of the foundation pit surrounding rock under the superposition of the adjacent river water level changes and ground loads be comprehensively evaluated, but also the potential instability trend of the soil-rock interface under the coupling of hydraulics and stresses can be captured, providing scientific support for safe construction under the complex working conditions of the deep and large foundation pit adjacent to the river, and laying the foundation for the redundancy analysis and intelligent stability assessment of the support structure.

[0065] Step S60 numbers the support components and simulates their local failures in sequence, records the maximum horizontal displacement, maximum vertical displacement or safety factor of the foundation pit after each failure as a function of the number of failed components, quantifies the redundancy of the support system and identifies key components.

[0066] All support components in the foundation pit support system are numbered in sequence to form a support component set: ,

[0067] in, represents the i-th supporting component, n represents the total number of supporting members.

[0068] In the numerical model, each support component is assigned a unique number attribute to achieve state control and response tracking of individual components, ensuring the feasibility of local failure simulation.

[0069] Select component sets in sequence One or more components in , set it to failure state and simulate the loss of its carrying capacity. The specific operations are: The initial stiffness of the component is recorded as , the initial bearing capacity is , after the setting is invalid: ,

[0070] in: Indicates the stiffness of the component after failure; Indicates the bearing capacity of the component after failure; Represents the minimum coefficient, usually taken as , which is used to approximately simulate complete failure.

[0071] After component failure, record the following deformation and stability indicators of the foundation pit surrounding rock or support system: Maximum horizontal displacement: , unit is m; Maximum vertical displacement: , unit is m; Safety factor: , which represents the stability reserve of the foundation pit in the current failure state, and the unit is dimensionless.

[0072] Increasing the number of failed components ,simulation The following relationship curve is obtained for the case where a component fails: and relationship; and relationship; and relationship.

[0073] The deformation and stability index of the foundation pit when the supporting components are not failed are set as the benchmark values: ,

[0074] are the maximum horizontal displacement, maximum vertical displacement and safety factor when there is no failure, respectively.

[0075] When the number of failed components is m, the redundancy change rate of the maximum horizontal displacement of the foundation pit is defined as: ,

[0076] in: It represents the percentage of the horizontal displacement increment of the foundation pit after m components fail, and the unit is %; It represents the maximum horizontal displacement after the failure of m components, in m; Indicates the initial maximum horizontal displacement, in meters.

[0077] Similarly, the redundancy change rate based on the safety factor is: ,

[0078] in: It indicates the reduction ratio of safety factor after m components fail, in %. It represents the safety factor after m components fail, and the unit is dimensionless.

[0079] Will and It is drawn as a function curve to evaluate the performance degradation trend of the support system under local failure and reflect the system redundancy and ultimate bearing capacity.

[0080] Determine a component Whether a component is a key component is determined by the deformation or safety factor mutation caused by its failure alone. A component is a key component if it meets any of the following conditions: Horizontal displacement mutation conditions: ,

[0081] Safety factor mutation conditions: ,

[0082] in: Representation component The horizontal displacement increment caused by failure, in m; Representation component The reduction in safety factor due to failure, dimensionless units; 、 Indicates the preset judgment threshold, with a typical value of 10%~20%.

[0083] Constitute a set of key components: ,

[0084] Finally, the redundancy change curve, key component numbers and their corresponding positions are output to determine the redundancy capacity limit of the support system, optimize component layout and parameter configuration, conduct construction quality control and real-time monitoring of key components, form emergency reinforcement and risk management plans for local failures, and ensure the safety and stability of the entire foundation pit construction process.

[0085] The prior art mentioned in the above background technology section and specific embodiments section of the present invention can be regarded as part of the present invention and used to understand the meaning of some technical features or parameters.

Claims

1. A three-dimensional geological structure modeling method for deep and large foundation pits in Linjiang area, characterized by: The method comprises the following steps: Obtain the physical and mechanical parameters and hydrogeological information of the deep excavation area in Linjiang River, collect data on the changes in Linjiang River water levels over the years and the water levels of groundwater observation wells, and combine ground loads with environmental information to generate data for a three-dimensional coupled analysis of the water surface, ground surface, and soil and rock surface. Based on the drilling and testing results, the spatial distribution of different soil and rock layers is divided, and the weak interlayers, fracture development zones or potential damage zones at the soil-rock interface are identified. The soil-rock interface is described using contact elements or weakened zone models. The change process of the Linjiang River water level from abrupt rise to temporary stability to slow drop is transformed into a time-varying seepage boundary condition. The influence of the time-varying water level on the pore water pressure and erosion of the foundation pit surrounding rock is described by the unsteady seepage equation. Based on the three-dimensional spatial characteristics of the surface topography and underlying rock and soil layers, a finite element or finite difference grid is created to characterize the mechanical and seepage properties of the soil, rock, and soil-rock interface, and dynamic water level and ground load boundary conditions are applied. According to the actual excavation sequence of the foundation pit and the support structure layout plan, the groundwater flow field and the evolution of the soil and rock deformation field in each excavation step are gradually unloaded and analyzed, and the coupling effect of the water surface, ground surface and soil and rock surface is integrated throughout the excavation process; The support components are numbered and their local failures are simulated in sequence. The maximum horizontal displacement, maximum vertical displacement or safety factor of the foundation pit after each failure is recorded as a function of the number of failed components. The redundancy of the support system is quantified and key components are identified.

2. The three-dimensional geological structure modeling method for deep and large foundation pits in Linjiang area according to claim 1 is characterized in that: The physical and mechanical parameters include the natural density, porosity, saturation, permeability, cohesion, internal friction angle and elastic modulus of each stratum.

3. The three-dimensional geological structure modeling method for deep and large foundation pits in Linjiang area according to claim 1 is characterized in that: The hydrogeological information includes the water level change data of the adjacent river over the years and the water level time series data recorded in the groundwater observation wells around the foundation pit.

4. The three-dimensional geological structure modeling method for deep and large foundation pits in Linjiang area according to claim 1 is characterized in that: The weak zone model reflects the weakness and damage characteristics of the soil-rock interface by adjusting the interface strength parameter or stiffness parameter.

5. The three-dimensional geological structure modeling method for deep and large foundation pits in Linjiang area according to claim 1 is characterized in that: The finite difference grid satisfies the following conditions: a) The grid density and cell size are adaptively set according to the stratum gradient, and a fine grid is used in the soil-rock interface area to improve local accuracy; b) The soil layer elements adopt tetrahedron or hexahedron elements suitable for porous media seepage and constitutive models. The rock mass elements consider the influence of cracks and introduce nested crack elements. c) Contact elements or weakening elements are set at the soil-rock interface to realize the friction, slip and hydraulic coupling behaviors of the interfaces between different materials.

6. The three-dimensional geological structure modeling method for deep and large foundation pits in Linjiang area according to claim 1 is characterized in that: The load boundary conditions meet the following conditions: a) Apply a constant head boundary condition to the riverside boundary to simulate the effect of river water seepage into the surrounding rock system; b) Set drainage conditions or constant flow boundaries at the bottom of the foundation pit and the far-field boundary to maintain hydraulic balance inside and outside the model; c) During the water level rise, the boundary head increases at the rate of the steep rise stage, remains unchanged during the time-stable period, and decreases linearly during the slow drop period.

7. The three-dimensional geological structure modeling method for deep and large foundation pits in Linjiang area according to claim 1 is characterized in that: After creating a finite element or finite difference mesh that can characterize the mechanical and seepage characteristics of the soil, rock mass, and soil-rock interface, and applying dynamic water level and ground load boundary conditions: The stability of the preliminary grid division and boundary condition setting is verified, and grid independence analysis is used to ensure that the influence of unit density on the calculation results is controllable. Local encryption is performed around the support structure and at the soil-rock interface.

8. The three-dimensional geological structure modeling method for deep and large foundation pits in Linjiang area according to claim 1 is characterized in that: After each excavation step, the construction and activation of the corresponding support components are simulated according to the support structure layout plan, including: Simulate support pile placement and apply stiffness and boundary constraints; Install anchor rods and apply prestressing force; Add sprayed anchors and internal support systems to apply constrained displacement or reaction force.

9. The three-dimensional geological structure modeling method for deep and large foundation pits in Linjiang area according to claim 1 is characterized in that: In each excavation step, comprehensive consideration should be given to: Seepage field and pore water pressure changes caused by water surface changes, The influence of ground load on the stress field of surrounding rock, Stress concentration and erosion evolution at soil-rock interface under seepage-deformation action.

10. The three-dimensional geological structure modeling method for deep and large foundation pits in Linjiang area according to claim 1 is characterized in that: After quantifying the redundancy of the support system and identifying key components, the system outputs a redundancy change curve, key component numbers, and their corresponding locations. This is used to: determine the redundancy capacity limit of the support system, optimize component layout and parameter configuration, conduct construction quality control and real-time monitoring of key components, and develop emergency reinforcement and risk management plans for local failures, ensuring the safety and stability of the entire foundation pit construction process.

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