Slope landslide risk identification and stability evaluation method considering excavation and rainfall infiltration coupling

Abstract

This invention relates to the field of geotechnical engineering and geological disaster prevention technology, and provides a method for slope landslide risk identification and stability evaluation considering the coupling effect of excavation and rainfall infiltration. The method includes the following steps: inputting geological survey data; establishing a geometric model and material zoning; determining unsaturated hydraulic parameters; performing steady-state seepage analysis to establish a steady-state initial field; performing unsteady-state infiltration analysis; calculating / correcting unsaturated shear strength parameters; conducting limit equilibrium method (LEM) and strength reduction method (SSR) analyses in parallel; extracting the most unfavorable slip surface; comparing and verifying the consistency of the LEM slip surface and the SSR slip surface, and outputting the slope risk level and early warning suggestions based on the verified results. This scheme achieves reliable identification of the instability moment, the most unfavorable slip surface, and the contribution of excavation / rainfall through the above method. It can be directly applied to slope risk classification and early warning, significantly improving the engineering applicability of the research results, and has advantages such as wide applicability and ease of engineering integration.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering and geological disaster prevention technology, specifically to a method for identifying and evaluating the stability of slope landslide risks by considering the coupling effect of excavation and rainfall infiltration. Background Technology

[0002] Toe excavation and rainfall infiltration are two key factors inducing landslides in mountainous areas. Toe excavation directly alters the slope geometry and weakens toe support, leading to stress redistribution and reduced stability, which is particularly pronounced under conditions of fractured rock, severe weathering, or thick overburden. Rainfall infiltration, on the other hand, continuously weakens the shear strength of unsaturated soil or weathered rock by increasing water content, pore water pressure, and reducing matrix suction. As the wetting front moves downward, the saturated zone at the toe may expand, and the groundwater level may rise, further reducing the safety factor and ultimately inducing instability. Under the coupled condition of "toe excavation + rainfall infiltration," accurately obtaining the pore pressure / suction field that evolves with rainfall over time, and further reliably identifying the most unfavorable slip surface and instability moment, are key technical issues in landslide risk identification and stability assessment.

[0003] Current engineering analyses often employ a step-by-step approach of "seepage first, then stabilization": first, the initial pore water pressure field is determined through steady-state seepage; then, unsteady-state saturated-unsaturated seepage calculations are performed with rainfall boundaries to obtain the pore pressure and suction distributions at different durations; finally, this data is imported into stability analysis to solve for the safety factor and critical slip surface. To characterize the strength attenuation caused by rainfall, studies commonly incorporate the contribution of matrix suction into the Mohr-Coulomb criterion to reflect the nonlinear characteristics of unsaturated strength. Regarding hydraulic parameters, soil-water characteristic curves and unsaturated permeability functions are frequently used to describe seepage behavior, and models such as Van Genuchten are used for fitting and extrapolation to solve the seepage governing equations.

[0004] While existing "seepage-stability" coupling methods are helpful in revealing the mechanism of rainfall-induced landslides, they still have shortcomings in simultaneously considering the combined effects of excavation and rainfall: First, there is a lack of a unified and reproducible process-oriented method, making it difficult to systematically handle the combined effects of "excavation-induced changes in morphology and support" and "rainfall-induced evolution of pore pressure / suction"; Second, the determination of the slip surface is highly subjective. The Limit Equilibrium Method (LEM) is greatly affected by the assumed slip surface and inter-strip force mode, while the Strength Reduction Method (SSR), although it can reflect the strain concentration zone, lacks a systematic verification and consistency criterion between its results and the safety factor and slip surface location obtained from LEM; Third, fully coupled hydraulic-mechanical analysis is usually computationally intensive and complex to implement. Some studies simplify the treatment of pore pressure-induced deformation effects in numerical implementation to reduce computational difficulty, but this may also introduce errors and uncertainties under certain working conditions, affecting the reliability of early warning thresholds and risk assessments.

[0005] Therefore, there is an urgent need to develop a slope stability evaluation method applicable to the coupled working condition of "slope toe excavation-rainfall infiltration" to realize a new method and system for landslide risk identification and slope stability evaluation, including seepage field evolution calculation, LEM / SSR dual-method comparison and verification, and reliable determination of the most unfavorable slip surface. Summary of the Invention

[0006] To address the problems existing in the background technology, this invention proposes a method for identifying landslide risks and evaluating stability of slopes that considers the coupling effect of excavation and rainfall infiltration. This method enables reliable identification of the instability moment, the most unfavorable slip surface, and the contribution of excavation / rainfall. It can be directly applied to slope risk classification and early warning, significantly improving the engineering feasibility of the research results. It has the advantages of wide applicability and ease of engineering integration.

[0007] To achieve the above objectives, the present invention adopts the following solution:

[0008] A method for identifying landslide risk and evaluating stability of slopes that considers the coupling effect of excavation and rainfall infiltration includes the following steps: Step 1: Obtain topographic and geological data of the slope, excavation parameters and rainfall data, and define at least two analysis conditions that include the state before and after excavation. Step 2: Establish a numerical model of the slope, divide it into material zones, and assign mechanical parameters to each zone; Step 3: Determine the unsaturated hydraulic parameters of the slope overburden and weathered rock mass; Step 4: Perform steady-state seepage analysis based on the numerical model to obtain the initial groundwater level and pore pressure field; Step 5: Based on the initial groundwater level and pore pressure field, perform unsteady infiltration analysis to obtain dynamic evolution data of pore water pressure field, matrix suction field and saturation field during rainfall. Step 6: Based on the dynamic evolution data, calculate and correct the unsaturated shear strength parameters; Step 7: Based on the dynamic evolution data and the corrected shear strength parameters, perform limit equilibrium method LEM and strength reduction method SSR analysis in parallel to obtain SSR displacement, strain field and LEM slip surface; Step 8: Based on the strain field obtained from SSR analysis, extract the equivalent plastic strain concentration zone to determine the SSR slip surface; Step 9: Compare and verify the consistency between the LEM slip surface and the SSR slip surface, and output the slope risk level and early warning suggestions based on the verification results.

[0009] Optionally, in step 1, the defined analysis conditions also include the pre-rainfall state and the post-rainfall state, and are combined with the pre-excavation and post-excavation states to form multiple sets of comparative conditions; the topographic and geological data include slope topographic data, stratigraphic distribution data, groundwater level data, and lateral recharge head data; the excavation condition parameters include pre-excavation slope parameters, post-excavation slope parameters, and retaining structure layout parameters; the rainfall process data includes historical rainfall process data and designed rainfall process data.

[0010] Optionally, step 3 specifically includes: conducting indoor tests or inversion analysis on the overburden and weathered rock mass to obtain the soil-water characteristic curve SWCC, and using the Van Genuchten model to fit the volumetric water content-matrix suction relationship corresponding to the soil-water characteristic curve SWCC; further calculating the unsaturated permeability function based on the soil-water characteristic curve SWCC, and simultaneously determining the saturated permeability coefficient, anisotropic permeability coefficient and water storage modulus.

[0011] Optionally, in step 5, the rainfall process is discretized into an intensity-duration sequence, which is then converted into an hourly application of the top surface flux boundary.

[0012] Optionally, step 6 specifically includes: in the slope stability calculation, introducing an expression for unsaturated shear strength based on the concept of effective stress and the Mohr-Coulomb criterion, considering the contribution of matric suction, and converting the matric suction field into strength parameters, the conversion formula being: , Where σ′ is the equivalent effective normal stress of the unsaturated soil (or weathered rock overburden) at the calculation point / slip surface; σ is the total normal stress (total normal stress) at that point (or the bottom surface of the slice / potential slip surface). u a Pore ​​gas pressure; u w Pore ​​water pressure; S r Saturation; τ is the effective stress parameter / saturation function. f φ is the shear strength; c′ is the effective cohesion; φ′ is the effective internal friction angle.

[0013] Optionally, in step 7, the Morgenstern-Price method is used to perform limit equilibrium analysis, output the safety factor at different times and search for the corresponding critical slip surface, and constrain the search range by setting the inlet and outlet regions of the slip surface; the instability criterion of the strength reduction method SSR analysis is the non-convergence of numerical calculation iteration, the safety factor is the strength reduction coefficient when the slope reaches the critical state, and the output results are displacement and plastic strain data.

[0014] Optionally, step 8 specifically involves searching for the maximum value of the equivalent plastic strain in each calculated column along the vertical direction of the model, and then connecting and smoothing these extreme points in sequence to form an SSR slip surface.

[0015] Optionally, in step 9, the consistency check includes the safety factor FS obtained from LEM and SSR and the geometric difference of the slip surface. If the difference exceeds the safety factor difference threshold or the slip surface geometric difference threshold, the calculation parameters of the limit equilibrium method LEM are adjusted and recalculated until the consistency requirements are met. The safety factor difference threshold is: , The geometric difference threshold of the slip surface is: , in, H is the average normal distance, and H is the slope height.

[0016] Optionally, step 9 further includes: quantifying the contribution of slope toe excavation and rainfall infiltration to the reduction of slope stability based on the changes in safety factors under different comparative working conditions, wherein the contribution decomposition process is as follows: At the same time or under the same rainfall duration, assuming 00 The safety factor before excavation and before rainfall is used as a benchmark. 10 The safety factor is calculated as the sum of the excavation time and the rainfall time. 01 ( (This refers to the period before excavation plus rainfall duration) t The safety factor; 11 ( (This refers to the period after excavation plus rainfall duration) t Safety factor (for coupled operating conditions); The total decrease expression is: , The excavation contribution expression is: , The expression for the contribution of rainfall is: , Contribution can be expressed as a percentage: , in, Contribution to excavation; Contribution to rainfall; Contribution to coupling interaction; ΔFS tot The decrease in the overall safety factor; Δ FS exc The reduction in safety factor due to excavation; Δ FS rain∣exc This represents the decrease in the safety factor caused by rainfall during excavation. The reduction in the safety factor corresponding to the coupled interaction term.

[0017] Optionally, in step 9, the slope risk level and early warning recommendations include: Level IV Risk (Green / Stable State): When When the water level is ≥1.25, routine inspections should be conducted in conjunction with pre-rain ditch clearing measures. Level III Risk (Yellow / Basically Stable State): When 1.15 ≤ <1.25 or / When the rate of descent exceeds the threshold, encrypted monitoring is implemented, excavation is restricted, and drainage and covering structures are deployed. Level II Risk (Orange / Unstable State): When 1.05 ≤ When the load is less than 1.15, measures such as work stoppage or load reduction, emergency drainage (including drainage diversion, wellpoint dewatering, and intercepting drainage ditches), temporary support, and anchor cable reinforcement shall be taken. Level I Risk (Red / Unstable State): When If the value is less than 1.05 or the SSR fails to converge and the displacement suddenly increases, immediately organize personnel to evacuate, implement area lockdown, and carry out emergency rescue and disposal.

[0018] The beneficial effects of this invention are as follows: This scheme simultaneously considers the changes in geometric and support conditions caused by excavation, as well as the evolution of pore pressure / suction caused by rainfall infiltration, within the same process. It determines the initial field through steady-state seepage, characterizes the time-varying seepage field through unsteady-state infiltration, and performs stability analysis at each moment. This allows for the acquisition of the continuous evolution of the safety factor over rainfall duration, thereby more accurately identifying the critical instability moment and the most dangerous stage. Specifically, it includes: (1) This scheme introduces unsaturated seepage and soil-water characteristic curves, which can explicitly characterize the strength degradation caused by suction attenuation and saturation zone expansion: an unsteady seepage model is established by using soil-water characteristic curves (SWCC) and unsaturated permeability function to output the spatiotemporal distribution of pore pressure, suction and saturation. In the stability analysis, the suction-strength relationship is incorporated into the shear strength calculation, so that the influence of rainfall on strength attenuation can be quantitatively reflected, which improves the physical rationality and interpretability of rainfall-triggered analysis and solves the problem that existing technologies only use simplified water level lines or empirical pore pressure coefficients, which are difficult to reasonably reflect the suction contribution.

[0019] (2) This scheme constructs a parallel calculation and consistency verification mechanism of the limit equilibrium method LEM and the shear strength reduction method SSR, which significantly reduces the uncertainty brought about by a single method: the safety factor and the slip surface are output simultaneously under the same pore pressure field, the difference is quantitatively verified, and self-consistent verification is achieved by adjusting the search domain, mesh refinement or boundary constraints, thereby improving the reliability and interpretability of the evaluation results.

[0020] (3) This scheme can automatically extract the slip surface based on the plastic strain concentration zone, which can reduce subjective assumptions and improve the accuracy of slip surface positioning: using the equivalent plastic strain (or shear strain) concentration zone output by SSR, the potential failure zone is automatically extracted by the rule of "vertical (or normal) extreme point search - line fitting - smooth constraint", so as to obtain the critical slip surface that is more consistent with the mechanical evolution process, and can be further used for the entry / exit slip zone setting of reverse constraint LEM, improving the engineering credibility and repeatability of slip surface identification. It overcomes the problem that the traditional LEM slip surface search is prone to "too shallow, too deep or deviating from the actual failure zone" if there is a lack of constraints.

[0021] (4) This scheme can quantitatively decompose the contribution of excavation and the contribution of rainfall: by comparing the multi-condition combination of "before / after excavation + before / after rainfall", the decomposition amount of the safety factor decrease is extracted to form the excavation contribution and rainfall contribution index; and further output the critical rainfall duration, critical infiltration flux or critical safety factor time, providing a quantitative basis for construction organization, drainage and support reinforcement.

[0022] (5) The output indicators of this scheme are highly engineered and can be directly used for risk classification and early warning: The output of this scheme not only includes the safety factor and critical slip surface, but also provides: the expansion range of the saturation zone, the range of the suction attenuation zone, the location of the plastic strain concentration zone, the critical instability moment, and the risk level and early warning suggestions. Compared with the traditional results that only provide a single safety factor, this invention forms a complete chain output of "hydraulic evolution - strength degradation - stability change - failure zone location", which facilitates on-site monitoring deployment and early warning threshold setting, and improves the feasibility of the results.

[0023] (6) This solution has a wide range of applications and is easy to integrate into engineering projects: This method can be applied to various scenarios such as highway / railway slope cutting, mine slope, urban construction slope, foundation pit slope and reservoir bank slope; it can be integrated with commonly used seepage and stability analysis platforms to realize automated calculation and batch working condition assessment, and it can also be connected with rain gauges, pore pressure gauges, inclinometers and surface displacement monitoring data to realize a closed loop of engineering applications from evaluation to early warning. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the overall process of the method of the present invention. Figure 2 This is a comparative schematic diagram of the computational domain, boundary conditions, and geometric changes of the retaining / excavation before and after excavation in an embodiment of the present invention. (a) is a schematic diagram of the computational domain, boundary conditions, and geometric changes of the retaining / excavation before excavation, and (b) is a schematic diagram of the computational domain, boundary conditions, and geometric changes of the retaining / excavation after excavation. Figure 3 This is a schematic diagram of pore pressure / suction and saturation zone expansion at different times obtained from unsteady-state seepage calculations in an embodiment of the present invention, wherein (c) is... t A schematic diagram of pore pressure / suction and saturation zone expansion at =0h, (d) is... t A schematic diagram of pore pressure / suction and saturation zone expansion at 9h, (e) is... t Schematic diagram of pore pressure / suction and saturation zone expansion at 27h; Figure 4 This is a schematic diagram illustrating the variation and differences in FS obtained by the Limit Equilibrium Method (LEM) and the Intensity Reduction Method (SSR) with rainfall duration in an embodiment of the present invention. Figure 5 This is a schematic diagram of the numerical model in an embodiment of the present invention. Detailed Implementation

[0025] To make the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the given embodiments are merely one implementation method and do not represent all embodiments.

[0026] This invention provides a method for identifying slope landslide risk and evaluating stability that considers the coupling effect of excavation and rainfall infiltration. This method aims to reliably identify the instability moment, the most unfavorable slip surface, and the contribution of excavation / rainfall.

[0027] This example uses the SEEP / W (saturated-unsaturated seepage) and SLOPE / W (LEM) modules in GeoStudio software to implement unsaturated seepage and limit equilibrium (LEM) stability analysis. At the same time, the COMSOL Multiphysics finite element platform is used to implement strength reduction (SSR) stability analysis by means of global equations or optimization of unknown parameters, and solves the reduction factor (safety factor).

[0028] like Figure 1 The overall process includes data input → establishing numerical models before / after excavation → determining unsaturated hydraulic parameters (SWCC / HCC) → calculating the initial groundwater level and pore pressure field based on steady-state seepage → calculating the time-varying pore pressure / suction / saturation field based on unsteady-state rainfall infiltration → performing LEM and SSR stability calculations in parallel → extracting / correcting the slip surface based on the equivalent plastic strain concentration zone → verifying the consistency of the two methods and outputting risks.

[0029] Specifically, it includes the following steps: Step 1, Geological Survey Data Input: Acquire topographic and geological data of the slope, excavation parameters, and rainfall data, and define at least two analysis conditions including pre-excavation and post-excavation states. Furthermore, the defined analysis conditions also include pre-rainfall and post-rainfall states, and are combined with these pre-excavation and post-excavation states to form multiple sets of comparative conditions to quantify the contribution of excavation and rainfall to stability.

[0030] The topographic and geological data include slope topographic data, stratigraphic distribution data, and hydrogeological data (groundwater level data and lateral recharge head data); the excavation condition parameters include excavation geometric parameters (slope parameters before / after excavation) and retaining structure (such as retaining walls) layout parameters; the rainfall process data includes historical rainfall process data and designed rainfall process data.

[0031] Step 2, Establish Geometric Model and Material Zoning: Establish a two-dimensional plane strain or three-dimensional slope numerical model, and divide the material into zones according to the degree of weathering or soil layers, such as... Figure 5 .

[0032] As one example, such as Figure 2A two-dimensional plane strain model was constructed, with a computational domain of 91.8 m in the X direction and 55.5 m in the Y direction. Geometric models were established before and after excavation to compare the effects of excavation. Furthermore, regarding stratification and structure: the strata were zoned according to weathering degree and engineering structures, with the example including five types of materials: silty clay, completely weathered slate, strongly weathered slate, moderately weathered slate, and retaining walls (or anti-sliding structures). Regarding the constitutive model: the materials adopted the Mohr-Coulomb elastoplastic foundation model, and the retaining walls were designed as high-strength, low-permeability elastic or rigid bodies. Regarding the mesh: a triangular unstructured mesh was used, with local densification in the excavation-aft area, stratum interface, and near the retaining walls to capture pore pressure gradients and plastic strain concentration zones.

[0033] Step 3: Determine the unsaturated hydraulic parameters.

[0034] The core mechanism of rainfall infiltration triggering landslides is as follows: During rainfall infiltration, the wetting front continuously advances, causing a decrease in matrix suction. Simultaneously, it promotes the continuous expansion of the local saturated zone and an increase in pore water pressure. The combined effect of these multiple factors ultimately leads to a decrease in the soil's shear strength, thereby inducing a landslide. Current technologies only use simplified water level lines or empirical pore pressure coefficients, which often fail to reasonably reflect the contribution of matrix suction, resulting in biased analyses of the impact of rainfall infiltration on landslide triggering and a lack of sufficient physical rationality. Therefore, this embodiment introduces the soil-water characteristic curve (SWCC) and the unsaturated permeability function into the seepage calculation framework.

[0035] Specifically, laboratory tests or inversion analyses were conducted on the overburden and weathered rock mass: the soil-water characteristic curve (SWCC) was obtained using the axis translation method, and the volumetric water content-matrix suction relationship corresponding to the SWCC was fitted using the Van Genuchten model; parameters included residual volumetric water content. θr saturated volumetric water content θs and curve parameters α , n and take m= 1 1 / n Where m is the curve shape parameter (related to pore size distribution); then the unsaturated permeability coefficient function (HCC) is estimated by SWCC, given the saturated permeability coefficient. ks The permeability coefficient as a function of matrix suction was subsequently derived. kw To improve the stability of numerical solutions.

[0036] Step 4: Perform steady-state seepage analysis to establish the steady-state initial field. With the goal of establishing the initial groundwater level and pore pressure field, this analysis obtains the initial groundwater level (GWL) and pore pressure distribution characteristics. The boundary conditions are set based on actual engineering conditions: as one embodiment, the steady-state seepage setting includes a total water head of 37 m on the left and 2.6 m on the right sides of the side boundary, an impermeable bottom boundary, and free atmosphere at the top boundary. After excavation, a pressure head is applied at the slope toe in the model to simulate the influence of the retaining wall on the groundwater level. The steady-state groundwater level and initial pore pressure / suction distribution are output as the initial conditions for unsteady infiltration.

[0037] Step 5: Perform unsteady infiltration analysis: Based on the steady-state initial field established in Step 4, apply the rainfall infiltration flux boundary to carry out unsteady saturated-unsaturated seepage calculations, and obtain dynamic evolution data of pore water pressure field, matrix suction field and saturation field during rainfall.

[0038] As one embodiment, the infiltration flow of unsteady rainfall adopts an unsaturated seepage control equation, taking into account the anisotropic permeability coefficient. kx , ky Total head H Boundary flux Q and the water storage modulus derived from SWCC mw A specified flux, estimated hourly, is applied to the top boundary, and simulated rainfall infiltration is applied segmentally according to time intervals. Typical times such as t=0h, 9h, 18h, and 27h are selected to output pore pressure-suction contour lines and 0℃ isotherms—similar to "state boundary lines"—to characterize the development of the infiltration front and the expansion of the saturated zone at the slope toe. Figure 3 The diagram shows the pore pressure / suction and saturation zone expansion at different times obtained from unsteady-state seepage calculations.

[0039] Step 6, Calculate / correct unsaturated shear strength parameters: Rainfall infiltration leads to increased pore pressure and decreased matrix suction, causing the "unsaturated shear strength" to decrease over time. Therefore, in slope stability calculations, the unsaturated shear strength expression based on the "effective stress concept + Mohr-Coulomb criterion" is introduced to fully reflect the contribution of matrix suction to soil shear strength and accurately reflect the nonlinear relationship between matrix suction and soil shear strength. The conversion expression is as follows: , Where σ′ is the equivalent effective normal stress of the unsaturated soil (or weathered rock overburden) at the calculation point / slip surface; σ is the total normal stress (total normal stress) at that point (or the bottom surface of the slice / potential slip surface). u a Pore ​​gas pressure; u w Pore ​​water pressure; S r Saturation; τ is the effective stress parameter / saturation function. f φ is the shear strength; c′ is the effective cohesion; φ′ is the effective internal friction angle.

[0040] Step 7: Perform limit equilibrium method (LEM) and strength reduction method (SSR) analyses in parallel.

[0041] The Limit Equilibrium Method (LEM) is a mature engineering application, facilitating the output of safety factors and slip surfaces, but it relies on assumptions about slip surface morphology and inter-strip forces. The Shear Strength Reduction Method (SSR) can output displacement and strain information, but under complex seepage conditions, it may yield different safety factors and slip surfaces than LEM. This embodiment calculates LEM and SSR in parallel under the same pore pressure field, forming a "dual-method cross-checking" mechanism to reduce the uncertainty of a single method. Figure 4 The changes and differences in FS obtained from LEM and SSR with rainfall duration are shown.

[0042] Specifically, LEM stability analysis is performed to obtain the LEM slip surface: Based on the limit equilibrium method of LEM, the safety factor at different times is calculated using the pore pressure field and the reduced strength parameters, and the corresponding critical slip surface is searched. During the slip surface search, due to the limited availability of in-situ borehole core data, entry-exit zones are set as a priori constraints to reduce subjectivity. The safety factor FS is defined as the ratio of the shear strength to the mobilization shear stress on the slip surface.

[0043] SSR stability analysis was performed: the model was set with horizontal constraints on the side boundaries, full constraints at the bottom, and free at the top. The initial stress field was first used to eliminate the influence of gravity disturbance through self-weight stress balance. The failure to converge within a specified number of iterations was used as the instability criterion. The reduction coefficient was then used. Nr Synchronous reduction of cohesion as a control parameter c With internal friction angle φ Solve and optimize using global equations in COMSOL Nr Until instability occurs, and the safety factor is calculated. FS.

[0044] Step 8: Extract the most unfavorable slip surface: Under the combined effects of rainfall infiltration and excavation, the slip surface may exhibit complex morphologies such as non-circular arcs, layered control, or involvement of trailing edge traction cracks. Traditional LEM search is prone to problems such as "positional deviation or over-idealization." This step extracts the equivalent plastic strain cloud map or shear strain zone from the SSR analysis results. By searching for the maximum value of the equivalent plastic strain in each calculated column along the vertical direction of the model, and connecting and smoothing these extreme points sequentially, an SSR slip surface is formed. Based on this, the slip surface search of LEM is corrected / constrained to improve the consistency between the spatial location of the slip surface and the deformation characteristics in the field.

[0045] Step 9: Compare and verify the consistency between the LEM slip surface and the SSR slip surface, and output the slope risk level and early warning suggestions based on the verification results.

[0046] Specifically, consistency comparison and verification are carried out: the numerical differences of the safety factor FS obtained by the limit equilibrium method (LEM) and the strength reduction method (SSR) and the geometric differences of the slip surface are quantitatively compared; when the differences exceed the set thresholds (including the safety factor difference threshold and the slip surface geometric difference threshold), the entry or exit slip zone of LEM is automatically adjusted, and the model is recalculated after mesh refinement and boundary condition refinement until the calculation results meet the consistency requirements.

[0047] As one embodiment, comparing the safety factor FS and slip surface geometry differences obtained from LEM and SSR under the same rainfall duration, calculations / example calculations show that the FS difference before excavation is approximately 2.9%, and after excavation, approximately 2.6%, with the difference mainly stemming from the slip surface morphology. The SSR method is more conservative and can provide an earlier instability warning time (e.g., 4 h vs. 10 h). Based on this, SSR is used as the warning sensitive side, and LEM as the engineering verification side, forming a "dual threshold" output. The safety factor difference threshold is: , The geometric difference threshold of the slip surface is: , in, H is the average normal distance, and H is the slope height.

[0048] Excavation pushes the slope from a stable state close to its critical point. Rainfall infiltration reduces suction and increases saturation, ultimately triggering instability. Therefore, a quantitative comparison of four working conditions—before / after excavation and before / after rainfall—is used to clarify the contribution of excavation and rainfall to slope instability, providing a basis for construction control indicators and rainfall early warning thresholds. The contribution decomposition process is as follows: Assuming (at the same moment or during the same rainfall duration) 00 The safety factor (benchmark) is calculated before excavation and before rainfall. 10 The safety factor is calculated as the sum of the excavation time and the rainfall time. 01 ( (This refers to the period before excavation plus rainfall duration) t The safety factor; 11 ( (This refers to the period after excavation plus rainfall duration) t Safety factor (for coupled operating conditions).

[0049] The total decrease expression is: , The excavation contribution expression is: , The expression for the contribution of rainfall is: , The contribution can then be expressed as a proportion: , in, Contribution to excavation; Contribution to rainfall; Contribution to coupling interaction; Δ FS tot The decrease in the overall safety factor; Δ FS exc The reduction in safety factor due to excavation; Δ FS rain∣exc This represents the decrease in the safety factor caused by rainfall during excavation. The reduction in the safety factor corresponding to the coupled interaction term.

[0050] The risk output should include at least the FS-time curve, the location of the most unfavorable slip surface, the extent of the saturated zone at the toe of the slope, the depth of the wetting front, and graded early warning information based on reference standards (e.g., FS=1.15 as the minimum applicable value). As one example, based on the minimum slope safety factor... and the rate of change of safety factor / Based on displacement response characteristics, the risk level is divided into four levels, and corresponding early warning and response measures are set: Level IV Risk (Green / Stable State): When When the water level is ≥1.25, routine inspections should be conducted in conjunction with pre-rain ditch clearing measures. Level III Risk (Yellow / Basically Stable State): When 1.15 ≤ <1.25 or / When the rate of descent exceeds the threshold, encrypted monitoring is implemented, excavation is restricted, and drainage and covering structures are deployed. Level II Risk (Orange / Unstable State): When 1.05 ≤ When the load is less than 1.15, measures such as work stoppage or load reduction, emergency drainage (including drainage diversion, wellpoint dewatering, and intercepting drainage ditches), temporary support, and anchor cable reinforcement shall be taken. Level I Risk (Red / Unstable State): When If the value is less than 1.05 or the SSR fails to converge and the displacement suddenly increases, immediately organize personnel to evacuate, implement area lockdown, and carry out emergency rescue and disposal.

[0051] This invention achieves coupled evaluation of the entire process of "excavation-rainfall infiltration," enabling the acquisition of the continuous evolution of the safety factor over rainfall duration, making the analysis results closer to real-world conditions. It introduces unsaturated seepage theory and soil-water characteristic curves, explicitly characterizing the strength degradation caused by suction attenuation and saturation zone expansion. Parallel cross-calibration using LEM and SSR significantly reduces the uncertainty introduced by a single method. Based on the plastic strain concentration zone, it can automatically extract the slip surface, reducing subjective assumptions and improving the accuracy of slip surface location. By quantitatively decomposing the excavation contribution and rainfall triggering contribution, it provides a basis for targeted decision-making on construction organization and remediation measures. Its output indicators have a high degree of engineering sophistication and can be directly applied to slope risk classification and early warning, facilitating the deployment of on-site monitoring schemes and the setting of early warning thresholds, significantly improving the engineering feasibility of the research results. It has advantages such as wide applicability and ease of engineering integration.

[0052] The specific embodiments of the present invention have been described in detail above with reference to the figures, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for identifying landslide risk and evaluating stability of slopes considering the coupling effect of excavation and rainfall infiltration, characterized in that, Includes the following steps: Step 1: Obtain topographic and geological data of the slope, excavation parameters and rainfall data, and define at least two analysis conditions that include the state before and after excavation. Step 2: Establish a numerical model of the slope, divide it into material zones, and assign mechanical parameters to each zone; Step 3: Determine the unsaturated hydraulic parameters of the slope overburden and weathered rock mass; Step 4: Perform steady-state seepage analysis based on the numerical model to obtain the initial groundwater level and pore pressure field; Step 5: Based on the initial groundwater level and pore pressure field, perform unsteady infiltration analysis to obtain dynamic evolution data of pore water pressure field, matrix suction field and saturation field during rainfall. Step 6: Based on the dynamic evolution data, calculate and correct the unsaturated shear strength parameters; Step 7: Based on the dynamic evolution data and the corrected shear strength parameters, perform limit equilibrium method LEM and strength reduction method SSR analysis in parallel to obtain SSR displacement, strain field and LEM slip surface; Step 8: Based on the strain field obtained from SSR analysis, extract the equivalent plastic strain concentration zone to determine the SSR slip surface; Step 9: Compare and verify the consistency between the LEM slip surface and the SSR slip surface, and output the slope risk level and early warning suggestions based on the verification results.

2. The method for landslide risk identification and stability evaluation of slopes considering the coupling effect of excavation and rainfall infiltration as described in claim 1, characterized in that: In step 1, the defined analysis conditions also include the pre-rainfall state and the post-rainfall state, which are combined with the pre-excavation and post-excavation states to form multiple sets of comparative conditions; the topographic and geological data include slope topographic data, stratigraphic distribution data, groundwater level data, and lateral recharge head data; the excavation condition parameters include pre-excavation slope parameters, post-excavation slope parameters, and retaining structure layout parameters; the rainfall process data includes historical rainfall process data and designed rainfall process data.

3. The method for landslide risk identification and stability evaluation of slopes considering the coupling effect of excavation and rainfall infiltration as described in claim 1, characterized in that: Step 3 specifically includes: conducting indoor tests or inversion analysis on the overburden and weathered rock mass to obtain the soil-water characteristic curve SWCC, and using the Van Genuchten model to fit the volumetric water content-matrix suction relationship corresponding to the soil-water characteristic curve SWCC; further, based on the soil-water characteristic curve SWCC, calculating the unsaturated permeability function, and simultaneously determining the saturated permeability coefficient, anisotropic permeability coefficient, and water storage modulus.

4. The method for landslide risk identification and stability evaluation of slopes considering the coupling effect of excavation and rainfall infiltration as described in claim 1, characterized in that: In step 5, the rainfall process is discretized into an intensity-duration sequence, which is then converted into an hourly application of the top surface flux boundary.

5. The method for landslide risk identification and stability evaluation of slopes considering the coupling effect of excavation and rainfall infiltration as described in claim 1, characterized in that: Step 6 specifically includes: In the slope stability calculation, an expression for unsaturated shear strength based on the concept of effective stress and the Mohr-Coulomb criterion is introduced. Considering the contribution of matric suction, the matric suction field is converted into strength parameters, and the conversion formula is as follows: ， Where σ′ is the equivalent effective normal stress of the unsaturated soil or weathered rock overburden at the calculation point or slip surface; σ is the total normal stress at that point; u a Pore ​​gas pressure; u w Pore ​​water pressure; S r Saturation; τ is the effective stress parameter or saturation function. f φ is the shear strength; c′ is the effective cohesion; φ′ is the effective internal friction angle.

6. The method for landslide risk identification and stability evaluation of slopes considering the coupling effect of excavation and rainfall infiltration as described in claim 1, characterized in that: In step 7, the Morgenstern-Price method is used for limit equilibrium analysis, outputting the safety factor at different times and searching for the corresponding critical slip surface. The search range is constrained by setting the inlet and outlet regions of the slip surface. The instability criterion of the strength reduction method SSR analysis is the non-convergence of numerical calculation iteration. The safety factor is the strength reduction factor when the slope reaches the critical state. The output results are displacement and plastic strain data.

7. The method for landslide risk identification and stability evaluation of slopes considering the coupling effect of excavation and rainfall infiltration as described in claim 1, characterized in that: Specifically, step 8 involves searching for the maximum value of the equivalent plastic strain in each calculated column along the vertical axis of the model, connecting these extreme points sequentially and smoothing them to form an SSR slip surface.

8. The method for landslide risk identification and stability evaluation of slopes considering the coupling effect of excavation and rainfall infiltration as described in claim 1, characterized in that: In step 9, the consistency check includes the safety factor FS obtained from LEM and SSR, and the geometric difference of the slip surface. If the difference exceeds the safety factor difference threshold or the slip surface geometric difference threshold, the calculation parameters of the limit equilibrium method LEM are adjusted and recalculated until the consistency requirements are met. The safety factor difference threshold is: ， The geometric difference threshold of the slip surface is: ， in, H is the average normal distance, and H is the slope height.

9. The method for landslide risk identification and stability evaluation of slopes considering the coupling effect of excavation and rainfall infiltration as described in claim 1, characterized in that: Step 9 further includes: quantifying the contribution of slope toe excavation and rainfall infiltration to the reduction of slope stability based on the changes in safety factors under different comparative working conditions. The contribution decomposition process is as follows: At the same time or under the same rainfall duration, assuming 00 The safety factor before excavation and before rainfall is used as a benchmark. 10 The safety factor is calculated as the sum of the excavation time and the rainfall time. 01 ( (This refers to the period before excavation plus rainfall duration) t The safety factor; 11 ( (This refers to the period after excavation plus rainfall duration) t The safety factor; The total decrease expression is: ， The excavation contribution expression is: ， The expression for the contribution of rainfall is: ， Contribution can be expressed as a percentage: ， in, Contribution to excavation; Contribution to rainfall; To contribute to the coupling interaction; Δ FS tot The decrease in the overall safety factor; Δ FS exc The reduction in safety factor due to excavation; Δ FS rain∣exc This represents the decrease in the safety factor caused by rainfall during excavation. The reduction in the safety factor corresponding to the coupled interaction term.

10. The method for landslide risk identification and stability evaluation of slopes considering the coupling effect of excavation and rainfall infiltration as described in claim 1, characterized in that, In step 9, the slope risk level and early warning recommendations include: Level IV risk, i.e., green or stable state: when When the water level is ≥1.25, routine inspections should be conducted in conjunction with pre-rain ditch clearing measures. Level III risk, i.e., yellow or basically stable state: when 1.15 ≤ <1.25 or / When the rate of descent exceeds the threshold, encrypted monitoring is implemented, excavation is restricted, and drainage and covering structures are deployed. Level II risk, i.e., orange or unstable state: when 1.05 ≤ When the load is less than 1.15, measures such as work stoppage or load reduction, emergency drainage, temporary support, and anchor cable reinforcement shall be taken. Level I risk, i.e., red or unstable state: when If the value is less than 1.05 or the SSR fails to converge and the displacement suddenly increases, immediately organize personnel to evacuate, implement area lockdown, and carry out emergency rescue and disposal.

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