Analysis method and equipment for slope instability mechanism

Abstract

The invention discloses a slope instability mechanism analysis method and equipment, and the method comprises the steps: carrying out the investigation of a to-be-researched slope, and determining the geological environment characteristics of the slope and the disaster damage type of the slope; the physical and mechanical properties of the slope soil body are studied; establishing a slope calculation model, and simulating the influence of different slope heights and slope ratios on the slope stability in an initial state by combining finite element numerical calculation with the slope calculation model and physical and mechanical property data of a slope soil body; external influence factors causing slope instability are analyzed, and the stability and instability mechanism of the slope under different external influence factors are simulated and analyzed through finite element numerical calculation in combination with the slope calculation model and the physical and mechanical property data of the slope soil body. According to the method, the internal logic relation and the synergistic effect of internal factors and external factors are fully considered, the internal law of slope rock mass instability failure is determined, accurate prediction and evaluation are made for slope instability analysis, and a basis is provided for subsequent establishment of a corresponding slope safety estimation method.

Description

Technical Field

[0001] The invention relates to the technical field of slope stability analysis, and in particular to an analysis method and equipment for a slope instability mechanism. Background Art

[0002] Highway slopes are slopes with a certain slope on both sides of the roadbed to ensure the stability of the roadbed. With the steady progress of highway construction, the stability risk of high slopes has become more and more urgent; this is not only reflected in the construction safety during the engineering construction phase, but also in the reasonable maintenance and operation safety during the operation phase. Once a highway slope disaster occurs, it will have a major impact on the safe passage of the highway and cause serious losses to the safety of people's property, especially for some medium and low-grade highways or old highways, which have low construction standards and weak protection. It is necessary to achieve a wider coverage while monitoring the high-risk slopes at fixed points.

[0003] Slope instability can be considered as the process of deformation, destruction and movement of slope rock and soil. The development process of slope disasters including landslides, debris flows, collapses, and rockfalls is essentially the process of redistribution of materials and energy in the landslide rock and soil tending to equilibrium. Slope instability and failure require two prerequisites: (1) the internal destructive movement of the slope can form a penetrating sliding surface; (2) the sliding force of the slope is greater than the anti-sliding force. The slope rock structure is the key factor controlling the deformation and failure mode of the slope and determines the geomechanical model of slope failure. Establishing a geological model of typical slope instability mode is of great significance for analyzing the laws of slope instability and evaluating stability. The geological model of slope failure comprehensively reflects the various geological factors that affect the stability of the slope. Conversely, the deformation and failure mode of the slope reflects the main characteristics of the geological model.

[0004] Due to the complexity and variability of the rock mass structure of the slope and the differences in the surrounding engineering geological environment, the slope failure modes are diverse. Domestic and foreign scholars have conducted a lot of research on the slope instability mode. The main factors affecting slope stability can be summarized into three categories: (1) Engineering geological environment factors: including topographic and geomorphic characteristics, engineering geological structure, hydrogeological conditions, and geostress field distribution; (2) Slope structural conditions: including slope spatial geometric characteristics, rock mass structural characteristics, and rock mass structural surface characteristics; (3) Various triggering factors, including heavy rainfall, earthquakes, engineering excavation or loading, etc. Among the above three types of factors, the first two are internal factors, and the third is external factors. The deformation and destruction of the slope are essentially the result of the combined action of internal and external factors. The internal factors are the geological and material basis conditions for the occurrence of slope instability, and the external factors are the triggering factors for the occurrence of slope instability. Slope instability is affected by many uncertain factors at the same time, and deformations of different scales and instability failures of different forms will occur. The influencing factors are complex and changeable. Only using traditional deterministic analysis methods to analyze the deformation evolution mechanism and process of slope engineering will result in unsatisfactory results and inaccurate evaluation. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem that the existing deterministic analysis method of slope instability analyzes the deformation evolution mechanism and process of slope engineering, and obtains inaccurate evaluation, and to provide an analysis method and equipment for the slope instability mechanism.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for analyzing the mechanism of slope instability comprises the following steps:

[0008] Conduct investigation on the slope to be studied to determine the geological environment characteristics and the types of slope disasters;

[0009] According to the geological environment characteristics of the slope and the types of slope damage disasters, the physical and mechanical properties of the slope soil are studied;

[0010] Establish a slope calculation model, and simulate the influence of different slope heights and slope ratios on slope stability under the initial state through finite element numerical calculation, combined with the slope calculation model and the physical and mechanical properties data of the slope soil;

[0011] The external factors that cause slope instability are analyzed. Through finite element numerical calculation, combined with the slope calculation model and the physical and mechanical properties of the slope soil, the stability and instability mechanism of the slope under different external factors are simulated and analyzed.

[0012] In the technical solution of the present invention, the geological environment characteristics of the slope and the type of slope disaster damage are obtained according to the survey situation, and the physical and mechanical properties of the slope soil are studied to provide basic parameter data for subsequent numerical simulation calculations; a slope calculation model is established, and the influence of different slope heights and slope ratios on the stability of the slope in the initial state is first simulated by finite element numerical calculation, and then the stability and instability mechanism of the slope under different external influencing factors are analyzed, and the deformation of the slope inside and outside the slope is mastered, so that the stability and damage evolution law of the slope can be known, and a basis is provided for the identification and early warning of the disaster risk of the slope. When analyzing the problem of slope instability, the present invention fully considers the inherent logical connection and synergistic effect of internal and external factors, determines the inherent law of slope rock instability and destruction, makes accurate predictions and evaluations for slope instability analysis, and provides a basis for the subsequent establishment of corresponding slope safety prediction methods.

[0013] As a preferred embodiment of the present invention, the geological environment characteristics of the slope and the types of slope disaster damage are determined through domestic and foreign literature and field investigations. The geological environment characteristics of the slope include topography, stratum lithology, climate environment, and seismic activity; the types of slope disaster damage include deformation, cracking, and landslide.

[0014] As a preferred embodiment of the present invention, the slope damage disaster type includes landslide. According to the morphological characteristics and mechanism of the landslide, the landslide includes one of rock layer landslide, residual slope accumulation soil landslide and soil-rock binary translation landslide.

[0015] As a preferred embodiment of the present invention, the method for studying the physical and mechanical properties of slope soil is: selecting soil on the slope to carry out indoor geotechnical tests such as particle grading, critical moisture content, and natural bulk density, and studying the basic physical properties, soil-water properties, permeability properties, and shear strength properties of soils with different degrees of weathering. The basic physical properties include moisture characteristics, density characteristics, and particle size characteristics. The soil-water properties and permeability characteristics include soil-water characteristic curves and unsaturated permeability coefficients. The shear strength properties include internal friction angles and cohesion.

[0016] As a preferred embodiment of the present invention, when calculating the unsaturated permeability coefficient, based on the constant head permeability test, the saturated permeability coefficient of the soil-rock mixture with different stone contents is measured, and combined with the soil-water characteristic curve of the soil, the Van Genuchten model is used to fit the model parameters to obtain the unsaturated permeability coefficient of the slope soil with different stone contents, thereby calculating the unsaturated permeability coefficient.

[0017] As a preferred embodiment of the present invention, a method for simulating the influence of different slope heights and slope ratios on slope stability in the initial state is as follows: numerical calculation is performed based on the unsaturated shear strength failure criterion related to matrix suction, specifically, according to the current suction field of the embankment, the suction level of each unit of the slope calculation model is determined, and the equivalent cohesion including the suction is calculated; then the current stress state is determined, and the shear strength contribution of the effective normal stress is calculated; it is determined whether instability failure occurs at the current shear strength level; if no instability occurs, the strength is further reduced; if instability occurs, the reduction is determined to be complete, and the position of the most dangerous sliding surface and the safety factor are determined.

[0018] As a preferred embodiment of the present invention, for a landslide that is a residual slope accumulation type soil landslide, when rainfall infiltrates, the unsaturated soil mechanics stability analysis method of the slope is: setting the relationship between the change of the embankment soil permeability parameters, suction parameters and humidity parameters, the seepage rules, the infiltration boundary conditions and the rainfall type, determining the initial humidity field and the suction field, calculating the transient humidity field and the suction field, determining the transient suction level of each unit, calculating the effective cohesion, calculating the embankment stress level, calculating the embankment shear strain or the characteristic point displacement, and then judging whether the instability judgment standard is met. If not, the reduction factor is adjusted and the effective cohesion is returned to be recalculated. If it is met, the most dangerous sliding surface position is determined and the safety factor is determined.

[0019] As a more preferred embodiment of the present invention, when simulating and analyzing the stability and instability mechanism of the slope under different external influencing factors, the numerical simulation analyzes the impact of rainfall on soil moisture content, the impact of rainfall on pore water pressure, the impact of rainfall on slope deformation and the impact of rainfall on slope safety factor.

[0020] As a preferred embodiment of the present invention, for soil-rock binary translational landslide, when simulating and analyzing the stability and instability mechanism of the slope under different external influencing factors, numerical simulation and limit equilibrium method are used to carry out binary slope failure mechanism analysis under water infiltration.

[0021] As a more preferred embodiment of the present invention, in the numerical simulation of soil-rock binary translation landslide, the slope strike width is taken as 1m and the displacement of the slope strike is limited to simulate plane strain analysis, and the normal displacement of the left, right and bottom of the slope model is limited. The constitutive model of silt and fully weathered rock adopts the Strainsoftening constitutive model, and the constitutive model of moderately weathered rock adopts the Mohr-Colum constitutive model. The calculation termination condition is that the ratio of the average unbalanced force of all model nodes to the average force acting on all nodes reaches 1.1×10 -4; When the sliding surface is shaped like an arc, the simplified Bishop method can be used to calculate the slope stability coefficient; when the sliding surface is shaped like a broken line, the transfer coefficient method and the Morgenstern-Price method can be used to calculate the slope stability coefficient, and the minimum value of the slope stability coefficient calculated by the two methods is taken.

[0022] As a more preferred embodiment of the present invention, the slope includes a binary slope of a gently inclined contact surface type and a steep inclined contact surface type slope. The numerical simulation analyzes the failure mechanism of the binary slope of the gently inclined contact surface type, the failure mechanism of the binary slope of the steep inclined contact surface type, the influence of the slope and the thickness of the overlying soil on the slope stability, the influence of the mechanical properties of the soil on the safety factor of the slope, and the influence of rainfall conditions on the safety factor of the slope.

[0023] As a preferred embodiment of the present invention, for rock bedding landslides, the Hoek-Brown failure criterion is integrated into the principle derivation of the Morgenstern-Price method during the numerical simulation process to calculate the slope safety factor.

[0024] As a more preferred embodiment of the present invention, when simulating and analyzing the stability and instability mechanism of the slope under different external influencing factors, the deformation law of the slope under the action of excavation unloading, the overall stability of the slope, and the reinforcement effect with / without anchoring are analyzed in the numerical simulation.

[0025] Another aspect of the present invention provides an electronic device, comprising at least one processor, and a memory communicatively connected to the at least one processor; the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the above-mentioned slope instability mechanism analysis method.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention provides an analysis method for the mechanism of slope instability. According to the survey results, the geological environment characteristics of the slope and the type of slope disaster damage are obtained, and the physical and mechanical properties of the slope soil are obtained by research, providing basic parameter data for subsequent numerical simulation calculations; a slope calculation model is established, and the influence of different slope heights and slope ratios on the stability of the slope under the initial state is simulated by finite element numerical calculation, and then the stability and instability mechanism of the slope under different external influencing factors are analyzed. The deformation of the slope inside and outside the slope can be mastered, and the stability and damage evolution law of the slope can be known, providing a basis for the identification and early warning of slope disaster risks. When analyzing the problem of slope instability, the present invention fully considers the inherent logical connection and synergistic effect of internal and external factors, determines the inherent law of slope rock instability and destruction, makes accurate predictions and evaluations for slope instability analysis, and provides a basis for the subsequent establishment of corresponding slope safety prediction methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic flow chart of the analysis method of the slope instability mechanism of the present invention;

[0029] Figure 2 It is the soil-water characteristic curve of soil-rock mixture;

[0030] Figure 3 is the unsaturated permeability coefficient of soil-rock mixture under different rock contents;

[0031] Figure 4 It is the curve of the stability coefficient of the binary slope with gentle contact surface changing with the analysis conditions;

[0032] Figure 5 The curve of the stability coefficient of the steep and inclined contact surface binary slope changes with the analysis conditions;

[0033] Figure 6 is the safety factor of soil-rock binary translation landslide with different thickness and slope;

[0034] Figure 7 is the safety factor of the soil-rock binary translation landslide model with different cohesion and internal friction angles;

[0035] Figure 8 The curve of the safety factor of soil-rock binary translation landslide model changing with rainfall depth;

[0036] Fig. 9 is the cumulative displacement of characteristic points under standard conditions for rock layer landslide;

[0037] Fig.10 is the change of safety factor during slope excavation in rock layer landslide;

[0038] Fig.11 is the maximum vector displacement during the slope excavation process in a rock layer landslide (with or without anchoring);

[0039] Fig.12 The change of safety factor during slope excavation in rock layer landslide (with or without anchoring); DETAILED DESCRIPTION

[0040] In order to more clearly describe the invention purpose, technical scheme and technical effect advantages in the specific implementation case of the present invention, the scheme in the specific embodiment will be described in detail in combination with the drawings of the specification of the present invention. The specific technical scheme involved in the following specific embodiments is only for a clear and complete description of the innovative technical scheme of the present invention. It is only a part of the specific implementation scheme that can be adopted by the present invention, not all embodiments, and should not be understood as a limitation on the innovative scheme of the present invention. Any scheme adopting the same inventive concept of the present invention should be included in the protection scope of the present invention.

[0041] Secondly, the description of the drawings in the specific embodiments of the present invention is only for the convenience of technical personnel to understand the solution of the present invention. The partial details in the drawings are for the convenience of clearly presenting the technical solution. It should not be considered that all technical features in the drawings must be included in the specific implementation cases, and the detailed features in the drawings should not be identified as additional limitations on the innovative technical solution of the present invention. The components in the various embodiments described and shown in the drawings can be combined and arranged according to different configurations, and these changes in combination and arrangement should be identified as part of the entire embodiment of the innovative solution of the present invention and included in the scope of protection of the present invention.

[0042] In summary, the schemes or descriptions presented in the specific embodiments and drawings of the present invention are not intended to limit the scope of protection claimed, but are merely selected embodiments / cases to help technicians understand the relevant innovative solutions. Based on these embodiments, all other equivalent or parallel embodiments obtained by those skilled in the art without creative work are within the scope of protection claimed by the present invention.

[0043] Example 1

[0044] This embodiment provides a method for analyzing the mechanism of slope instability. Figure 1 , including the following steps:

[0045] Conduct investigation on the slope to be studied to determine the geological environment characteristics and the types of slope disasters;

[0046] According to the geological environment characteristics of the slope and the types of slope damage disasters, the physical and mechanical properties of the slope soil are studied;

[0047] Establish a slope calculation model, and simulate the influence of different slope heights and slope ratios on slope stability under the initial state through finite element numerical calculation, combined with the slope calculation model and the physical and mechanical properties data of the slope soil;

[0048] The external factors that cause slope instability are analyzed. Through finite element numerical calculation, combined with the slope calculation model and the physical and mechanical properties of the slope soil, the stability and instability mechanism of the slope under different external factors are simulated and analyzed.

[0049] This embodiment uses XX region as a research object to study the mechanism of highway slope instability, and determines the geological environment characteristics of the slope and the type of slope disaster damage through domestic and foreign literature and field investigation. In terms of topography and geomorphology, the overall landform of XX region is a mountainous and hilly basin landform, which is basin-shaped. In terms of stratum lithology, the slope strata in XX region are mainly Permian, Carboniferous and Devonian, and the lithology is mainly composed of limestone, dolomite and its transitional rocks, mainly limestone, and the lithology is mainly tertiary mudstone and silty mudstone. In terms of climate and environment, XX region is located in low latitudes, with the Tropic of Cancer running through the middle, facing the tropical ocean in the south, connecting the Nanling Mountains in the north, and extending to the Yunnan-Guizhou Plateau in the west, belonging to the subtropical monsoon climate zone. The climate is warm, with abundant rainfall and sufficient sunlight. In summer, the sunshine time is long, the temperature is high, and the precipitation is high, while in winter, the sunshine time is short and the weather is dry and warm. Affected by the alternation of warm and humid air currents from the southwest and the modified cold air mass from the north, meteorological disasters such as drought, rainstorms, floods, tropical cyclones, gales, hail, thunderstorms, and low temperature (freezing) damage are common. At the same time, after studying 105 geological disaster risk points with poor stability on national and provincial trunk lines in XX region (with a scale of 1000m 3 The above) and 42 sections of road prone to geological disasters were investigated in detail. The types of geological disasters mainly include slope geological disasters represented by landslides, collapses, unstable slopes and mud-rock flows, and karst geological disasters represented by karst ground collapse. Through on-site investigation, the geological and hydrological conditions along the Leye to Baise Expressway and the basic conditions of the high slopes of the road cuts were summarized. Through literature research, the typical geological-environmental characteristics of the XX area were summarized. On the basis of an overview of the landslide types in the XX area, combined with the slope landslide conditions investigated on the spot, three typical slope landslide types along the project in the XX area were proposed according to the nature and damage characteristics of the landslide slopes: bedding rock landslide, residual slope accumulation soil landslide and soil-rock binary translation landslide.

[0050] According to the geological survey report and the results of the on-site investigation, a large amount of loose deposits such as blocks and gravels are accumulated on the slopes by relying on the strong weathering in the landslide area along the project. At the same time, the rock weathering products are accumulated on the spot or nearby, forming a soil-rock mixture of a certain thickness mainly composed of sand, clay, gravel and blocks. The soil body studied in this embodiment is a soil-rock mixture. The acquisition of the physical and mechanical parameters of the soil-rock mixture is usually based on testing the soil in the soil-rock mixture, and then multiplying it by a certain coefficient of variation (some are reduction coefficients, and some are enhancement coefficients). However, the soil-rock mixture is mostly residual slope deposits, landslide deposits and alluvial deposits, etc. The material composition is mainly loose deposits such as soil with gravel or broken stones, gravel or broken stones with soil, etc., and the medium structure has high variability, poor sorting, poor intergranular bonding, and strong permeability; the selection of the coefficient of variation has high uncertainty, and the physical and mechanical parameters finally calculated are not reliable.

[0051] The basic physical and mechanical properties of soil-rock mixtures were determined, soil-rock mixtures with different stone contents were configured, and the particle size characteristics, humidity characteristics, density characteristics, soil-water characteristics, permeability characteristics and shear strength characteristics of soil-rock mixtures were obtained through indoor geotechnical tests. Six representative slopes along the project were selected to carry out indoor geotechnical tests on the soil-rock mixtures at the soil sampling points, such as particle characteristics, limit moisture content, and natural bulk density. The soil samples were selected from the aforementioned typical soil-rock mixture samples, and the soil sample moisture content was the natural moisture content. The stone content was 30%, 40%, 50%, and 60%, respectively. The soil-water characteristics are expressed by the soil-water characteristic curve. The current soil-water characteristic curve tests are mostly in the low suction range. There is a certain deviation in the derivation of the soil-water characteristic curve in the full suction range using the limited data points in the low suction range. The pressure plate method is used to obtain the soil-water characteristic curve in the full suction range of the soil-rock mixture. Combined with the soil pore structure characteristics, the internal mechanism of the soil-water characteristic curve morphology of the soil-rock mixture is revealed, and a soil-water characteristic curve prediction model for the soil-rock mixture is constructed. The pressure plate method measures the suction of soil specimens through a pressure plate instrument. The GEO-Experts soil-water characteristic curve pressure plate instrument system is used. The system mainly consists of four parts: pressure plate instrument assembly, pressure control panel, vertical pneumatic loading system and water volume measurement system

[0052] The test results of the earth pressure plate test under different stone contents are plotted into a soil-water characteristic curve, such as Figure 2 As shown in the figure, it can be seen that the air intake values ​​of the soil-rock mixture under different stone contents are not much different. This is because when the stone content is 30%, there are obvious drainage channels in the soil-rock mixture, so the air intake values ​​of the soil-rock mixture under different stone contents are not much different. The residual suction value increases with the increase of stone content. At the same time, the larger the stone content, the larger the pores of the soil-rock mixture and the stronger the drainage capacity, resulting in a shorter transition section of the soil-water characteristic curve of the soil-rock mixture.

[0053] In establishing the relationship between soil matrix suction and rock content, this embodiment combines the above test results with the Van Genuchten model to obtain a soil-water characteristic curve. The Van Genuchten model formula is as follows:

[0054]

[0055] In the formula, S r is the effective saturation; Ψ is the matrix suction, in kPa; a, m, n are fitting parameters. The soil-water characteristic curve is fitted using the VG model, and the parameter fitting results of parameters a, m, n are shown in Table 1.

[0056] Table 1 Soil-water characteristic curve fitting parameters

[0057]

[0058] The saturated permeability coefficient cannot accurately characterize the permeability characteristics of the soil-rock mixture in an unsaturated state, and the measurement of the unsaturated permeability coefficient is relatively complicated. This embodiment is based on the constant head permeability test, combined with the soil-water characteristic curve to indirectly calculate the permeability coefficient function of samples with different stone contents, and study the influence of soil stone content on the unsaturated permeability characteristics of the soil-rock mixture. The constant head permeability test was carried out according to the "Highway Geotechnical Test Code" (JTG3430-2020), and the saturated permeability coefficient of the soil-rock mixture with different stone contents was calculated as shown in Table 2. It can be seen that with the deepening of the weathering degree of the slope rock and soil, the water content continues to decrease, the large pores in the soil-rock mixture decrease, the patency of the drainage channel decreases, and the permeability coefficient decreases.

[0059] Table 2 Permeability coefficient of soil-rock mixture

[0060]

[0061] The estimation model of unsaturated soil permeability coefficient uses the Gardner model to obtain the unsaturated permeability coefficient of soil-rock mixture. The formula of the Gardner model is as follows:

[0062]

[0063] Where: k is the unsaturated permeability coefficient, m / s; k S is the saturated permeability coefficient, m / s; S is the matrix suction, kPa; a and n are model parameters. Through the indoor variable head permeability test, the saturated permeability coefficient of soil-rock mixture with different stone contents and the soil-water characteristic curve of soil-rock mixture were measured by VG model fitting to obtain the values ​​of parameters a and n. The unsaturated permeability coefficient of soil-rock mixture with different stone contents was calculated as follows: Figure 3 shown.

[0064] The shear strength of soil-rock mixture is difficult to obtain through conventional direct shear test. Most of them are obtained through on-site push shear or compression shear axis test. The level of various influencing factors cannot be accurately controlled in the test, and there is also a lack of shear strength estimation model for soil-rock mixture. This embodiment analyzes the influence of stone content and water content on the unsaturated shear strength of soil-rock mixture through large-scale direct shear test. The test equipment uses shear-seepage coupling test machine, and the soil sample uses the aforementioned typical soil-rock mixture sample. The stone content of the soil sample is natural stone content, and the stone content is 30%, 40%, 50%, and 60% respectively. The performance under different water contents of 6%, 12%, 18%, and 24% (saturated) is studied. After research, the shear strength increases with the increase of stone content. When the vertical pressure is small, the increase of shear strength with the increase of stone content tends to be gentle; when the vertical pressure is large, the growth rate of shear strength is getting larger and larger. When the moisture content of the soil-rock mixture specimen is 12%, the shear strength increases first and then decreases with the increase of stone content, and the stone content corresponding to the shear strength peak is 50%. It can be seen that with the increase of moisture content, the shear strength increases first and then decreases. When the stone content is 30%, 40% and 50%, the peak value appears in the specimen with a moisture content of 12%, and when the stone content increases to 60%, the moisture content corresponding to the peak value is 18%, which shows that the increase of stone content increases the moisture content corresponding to the shear strength peak value.

[0065] According to the change of shear strength of specimens with different moisture contents under different moisture contents with vertical pressure, it can be obtained that as the vertical pressure increases, the shear strength also increases. By linearly fitting the failure envelope, the cohesion c and internal friction angle of different soil-rock mixture specimens can be obtained. As shown in Table 4. It can be seen that the cohesion increases first and then decreases with the increase of stone content, and the cohesion is the largest when the stone content is 50%; at the same stone content, the cohesion increases first and then decreases with the increase of water content, and the water content corresponding to the peak is between 12% and 18%. The internal friction angle generally shows an increasing trend with the increase of stone content; at the same stone content, the internal friction angle increases first and then decreases with the increase of water content, and the water content corresponding to the peak is about 12%. The soil-rock mixture specimen with a stone content of 50% and a water content of 12% has the largest cohesion (34.8kPa) and the second largest internal friction angle (26.3°). This shows that the slight weathering of the slope rock mass will increase the cohesion of the soil-rock mixture, and as the weathering degree deepens, the cohesion decreases. Once the slope rock mass begins to weather, the integrity of the rock mass decreases and the internal friction angle decreases.

[0066] Table 4 Cohesion and internal friction angle of soil-rock mixture specimens

[0067]

[0068] Based on the above data on the physical and mechanical properties of the slope soil, the following methods are used to analyze different landslide types:

[0069] (1) Residual slope soil landslide

[0070] In the initial state, the calculation model of the soil-like slope is the same as that of the rock. Considering 2 factors with 4 levels each, after completing the numerical simulation calculation of a total of 16 models, variance analysis is performed. The table of the calculation model is shown in Table 5. The upper layer of the rock slope is selected as strongly weathered sandstone, and the lower layer is weakly weathered sandstone. The material model is the Mohr-Coulomb model and the elastoplastic model, and the yield criterion is the Mohr-Coulomb criterion. The slope engineering stress-strain calculation parameters are shown in Table 6, which are from the engineering survey report and the corresponding indoor test.

[0071] Table 5 Influencing factors and level selection of initial state calculation model

[0072] level 1 2 3 4 Slope height 20 30 40 50 slope 1:0.8 1:1 1:1.2 1:1.4

[0073] Table 6 Soil property calculation parameters for soil slope engineering

[0074]

[0075] Based on the unsaturated shear strength failure criterion related to matrix suction, the corresponding numerical calculation is carried out. First, according to the current suction field of the embankment, the suction level of each unit is determined, and the equivalent cohesion including suction is calculated; then, the current stress state is determined, and the shear strength contribution of the effective normal stress is calculated; it is determined whether instability failure occurs at this shear strength level. If instability does not occur, the strength is further reduced; if instability occurs, the reduction is determined to be over, and the position of the most dangerous sliding surface and the stability safety factor are determined. The key to the stability analysis of soil-like slopes under rainfall infiltration lies in the determination of the transient suction field. Using finite element software, the relationship between the permeability parameters of the embankment soil, the change of the suction parameters and the humidity parameters, the seepage rules, the infiltration boundary conditions, and the rainfall type are set, and the transient suction field distribution after the rainfall ends can be calculated. Based on the new transient suction field, the stability safety factor of the embankment is calculated.

[0076] The influencing factors of residual slope accumulation soil landslide are groundwater and rainfall. This embodiment shows the influence of rainfall on slope stability. In the calculation, the calculation model is constructed with the slope section at K93+800. The model is 137m long and 73m high. Considering excavation, the net height of the slope is 61m, with a total of 5285 nodes and 5110 units. And 7 feature points of 73m, 72m, 71m, 70m, 60m, 40m and 20m are set vertically downward from the top of the slope. The material parameters of this report are obtained by integrating relevant engineering geological survey reports, design data and geotechnical tests in the previous text. The specific parameter values ​​are shown in Table 7. Among them, gravelly clay soil, that is, the cover layer, is divided into two levels of high weathering (stone content ≤50%) and poor weathering (stone content>50%). During rainfall, the stability of the slope is significantly affected by rainfall infiltration, and it is necessary to perform saturated-unsaturated seepage calculation on its cover layer to determine the safety factor of the slope in this process. The soil-water characteristic curve, an important parameter for unsaturated seepage calculation, was determined through the above test, and the permeability coefficient curve was fitted by the VG model. Three continuous rainfall intensity conditions were selected, and the rainfall intensities corresponding to heavy rain, rainstorm, and heavy rainstorm were 25, 50, and 100 mm·d, respectively. -1 , the calculation time is 10d.

[0077] Table 7 Material calculation parameters

[0078]

[0079] For the convenience of calculation, the slope finite element analysis model established in this embodiment is simplified with the following basic assumptions:

[0080] 1) The surface cover of the slope is relatively thin and can be ignored. The rock layers are completely continuous. At the interface between the layers, only the friction and displacement in the vertical direction are considered, and the puncture problem of the contact surface is not considered;

[0081] 2) The mechanical characteristics of rock materials are characterized by elastic modulus and Poisson's ratio; tuff and breccia are described by the Mohr-Coulomb model combined with the Hoek-Brown failure criterion;

[0082] 3) Horizontal (X) displacement constraints are applied on both sides of the model, and bidirectional (X and Y) displacement constraints are applied on the bottom of the model; horizontal displacement is positive to the right and negative to the left; vertical displacement is positive upward and negative downward. The default length unit is meter unless otherwise specified.

[0083] The unsaturated soil mechanics stability analysis process of soil-like slopes under rainfall infiltration is as follows: set the relationship between the permeability parameters, suction parameters and humidity parameters of the embankment soil, the seepage rules, the infiltration boundary conditions, and the rainfall type, determine the initial humidity field and suction field, calculate the transient humidity field and suction field, determine the transient suction level of each unit, calculate the effective cohesion, calculate the embankment stress level, calculate the embankment shear strain or characteristic point displacement, and then determine whether the instability judgment standard is met. If not, adjust the reduction factor and recalculate the effective cohesion. If it is met, determine the position of the most dangerous sliding surface and determine the stability safety factor.

[0084] 1.1 Correlation between initial state and slope stability

[0085] The safety factors of the slopes under 16 initial conditions were obtained by numerical calculation, and the calculation results are shown in Table 8. The analysis shows that the safety factor of the soil slope is negatively correlated with its own slope height and positively correlated with the slope ratio. When the slope ratio is constant, the safety factor of the soil slope decreases with the slope height, showing a good linear relationship, and the downward trend is basically the same, and the correlation with the slope height is -0.731; when the slope height is constant, the safety factor of the soil slope increases with the increase of the slope ratio, and the upward trend is basically the same, and the correlation with the slope ratio is 0.672. Compared with the stability factors of rock slopes, the safety factor of soil slopes is affected by slope height and slope ratio to a similar extent, and the influence of slope ratio is significantly increased.

[0086] Table 8 Soil slope stability under geometric factors

[0087]

[0088] 1.2 Effect of rainfall on soil moisture content

[0089] Based on the weathering gravel clay soil with a high degree of precipitation, the influence of rainfall on soil moisture content is analyzed, and the following conclusions are drawn from the calculation results:

[0090] 1) As rainfall continues, the water content of the slope surface increases significantly. From the perspective of spatial distribution, the areas with the fastest increase are the top platform, platforms at all levels and the lower half of the slope, which is consistent with the law of surface runoff;

[0091] 2) Under different rainfall intensities, the changing trends of moisture content are basically the same, but the affected ranges vary greatly. Under heavy rain intensity, the affected depth is about 1-2m, under rainstorm intensity, the affected depth is about 2-3m, and under very heavy rain intensity, the affected depth can reach about 4m.

[0092] 3) As the rainfall continues, the surface of the slope is saturated first, and the expansion range of the saturated zone is greater than the rainfall impact depth, indicating that after the surface of the slope is saturated, the infiltration rate of rainfall reaches its extreme value.

[0093] In order to quantitatively analyze the variation characteristics of slope volume moisture content during rainfall, the time course curve of moisture content at each measuring point was drawn, and the following results were obtained from the calculation results:

[0094] (1) From the perspective of rainfall impact depth, rainfall intensity and rainfall duration have different impacts on different measuring points. In general, the impact depth is positively correlated with the above two factors. However, based on existing calculations, the limit of the impact depth is basically around 4m, and the moisture content of deeper measuring points remains unchanged and is basically unaffected;

[0095] (2) Rainfall intensity has a significant impact on the growth rate of moisture content. Taking the soil on the slope surface as an example, it takes 96 hours to reach saturation under heavy rain conditions, 44 hours under torrential rain conditions, and only 24 hours under very heavy rain conditions. Other measuring points within the influence range also show similar patterns.

[0096] (3) The growth trend of soil moisture content basically shows a trend of first slow and then fast, which confirms that as the soil gradually approaches saturation, its infiltration rate also increases. This is particularly evident at the two measuring points at 72m and 71m. As the duration of rainfall increases, the deeper soil also begins to be gradually affected by the rainfall, and the greater the rainfall intensity, the faster this process is.

[0097] 1.3 Effect of rainfall on pore water pressure

[0098] Based on the analysis of the effect of rainfall on pore water pressure in gravelly clay soil with a high degree of weathering, the following conclusions are drawn from the calculation results:

[0099] 1) In the initial state, the pore water pressure is bounded by the groundwater level. It gradually increases downward, presenting a linear distribution, and gradually decreases upward, which is the matrix suction, with a maximum suction of -40 kPa;

[0100] 2) From the perspective of spatial distribution, the impact of rainfall on pore water pressure is mainly on the surface of the slope, and the impact depth is positively correlated with rainfall intensity and rainfall duration. The distribution law of the impact area is basically consistent with the distribution law of volume water content.

[0101] 3) The areas with more significant changes are mainly concentrated in the area within 4m from the slope surface, especially at the top platform, various platforms and the foot of the slope. Transient saturated areas appear in the above areas, the depth of the saturated zone does not exceed 2m, and the pore water pressure also changes from negative to positive.

[0102] In order to quantitatively analyze the variation characteristics of the slope pore water pressure during rainfall, the time course curves of the pore water pressure at each measuring point were drawn, and the following results were obtained from the calculation results:

[0103] 1) From the perspective of spatial distribution, the impact of rainfall intensity and rainfall duration on pore water pressure at different measuring points varies. Overall, the impact depth is positively correlated with the above two factors. The maximum impact depth is about 4m;

[0104] 2) Rainfall intensity has a significant impact on the growth rate of pore water pressure, and its development process is similar to that of volumetric water content. Except for the surface soil, other measuring points within the influence range also show similar laws. The development processes of volumetric water content and pore water pressure can verify each other.

[0105] 3) Unlike the volumetric water content, the growth trend of pore water pressure shows a "slow-fast-slow" trend, especially at the 72m measuring point, which has an obvious inflection point. The greater the rainfall intensity, the earlier the inflection point appears. Moreover, under the surface soil, as the rainfall continues, pore water pressure appears, indicating that the soil is completely saturated within this range, forming a transient saturated zone.

[0106] 1.4 Effect of rainfall on slope deformation

[0107] The influence of rainfall on slope deformation is analyzed based on gravelly clay soil with a high degree of weathering. The following conclusions are drawn from the calculation results:

[0108] 1) After excavation and unloading, the ground stress is fully released. After 5 days of load rebalancing, the initial state of the calculation of the influence of rainfall on slope deformation is set. At this time, there is no significant deformation of the slope;

[0109] 2) The deformation trends of the slopes under different rainfall intensities are relatively similar. From the perspective of spatial distribution, the impact of rainfall and self-weight stress on the slope is mainly concentrated at the top and foot of the slope, with a deformation of approximately 1 to 2 cm. From the perspective of stratum distribution, it is mainly concentrated in the gravel clay layer, and is significantly higher than the deformation of rock layers with different weathering degrees.

[0110] 3) The action mechanisms of the two areas with more concentrated strains at the top and toe of the slope are not exactly the same. Judging from the Y-direction (vertical) displacement, the toe of the slope has a more significant uplift deformation, which should be the manifestation of the overall deformation caused by the self-weight stress; while the deformation trend of the surface layer where the deformation is concentrated at the top of the slope is not clear, but it can be basically determined that it is caused by the decrease in the deformation modulus of the surface layer of the slope caused by rainfall, and the uplift phenomenon at the top of the 4th and 5th level slopes should be caused by the pushing effect after the surface soil slides down, which indicates that there is a hidden danger of shallow surface landslides in the soil layer at the top of the slope.

[0111] In order to quantitatively analyze the changing characteristics of slope displacement during rainfall, the time history curves of pore water pressure at each measuring point were drawn, and the following results were obtained from the calculation results:

[0112] 1) From the overall trend of change, as the rainfall continues, the horizontal and vertical displacements of each feature point show an increasing trend, but this trend is significantly different at different measuring points. Among them, the change trend of feature points 1, 2, and 3 is more obvious, generally 2 to 3 cm, and feature point 1 is the most prominent, with a maximum displacement of nearly 4 cm. Analysis shows that these feature points are located in gravel clay layers and are significantly affected by rainfall, while feature points 4, 5, and 6 located in sandstone layers have smaller deformations, with deformations within 1 cm, and are not significantly affected by rainfall;

[0113] 2) The rainfall intensity and displacement are positively correlated as a whole. As the rainfall intensity increases, the slope displacement increment also increases. This phenomenon is also significantly reflected in the gravel clay layer, but there is basically no significant change in the rock layer.

[0114] 3) The horizontal displacement and vertical displacement of different feature points also show a certain correlation. The horizontal displacement is slightly larger than the vertical displacement. The horizontal displacement shows an overall trend of deviating from the slope, while the vertical displacement shows a downward deformation trend. These deformation characteristics indicate that with the continuation of rainfall, the slope displacement continues to increase, and the risk of local or overall instability is also increasing.

[0115] 1.5 Effect of rainfall on slope safety factor

[0116] Compared with the influence of rainfall on the saturated-unsaturated state of the slope, the change of the slope safety factor caused by strength reduction has a more direct and intuitive impact on the stability of the slope. By analyzing the change trend of the safety factor under three different rainfall conditions, the following conclusions can be drawn: Selecting the most unfavorable working condition, the most unfavorable sliding surface of the slope does not appear in the shallow surface of the slope caused by conventional rainfall. The most unfavorable sliding surface is roughly 10m below the surface of the slope, with a 45° arc distribution. This should be the effect of the slope protection structure. However, this does not mean that rainfall has no effect on the slope. A careful analysis shows that there are still a small number of potential sliding surfaces with a safety factor of 1 to 1.1 within the range of 3 to 5m in depth. These sections also have a high risk of instability. The analysis shows that the existence of the slope protection structure can better avoid the risk of shallow landslides caused by short-term heavy rainfall, but if the rainfall lasts too long, the risk of slope instability still exists.

[0117] The slope safety factor showed a downward trend under the action of rainfall, but the rate of decline was significantly different and positively correlated with the rainfall intensity. -1 ), the rainfall lasted 234 hours, and the slope became unstable; under heavy rain conditions (50 mm·d -1 ), the rainfall lasted for 130 hours, and the slope became unstable; under heavy rain conditions (100 mm·d -1), the rainfall lasted for 62 hours and the slope became unstable; and there was a relatively obvious inflection point under heavy rain and rainstorm conditions. After the inflection point, the rate of decrease of the safety factor of the slope increased, which should be paid attention to in the later monitoring process.

[0118] The critical rainfall condition that causes slope instability is fitted with a power function to obtain the slope instability critical rainfall criterion curve (ID curve). The fitting formula is as follows:

[0119] I=6041.38×D -0.993

[0120] Where I is the rainfall intensity, in mm·d -1 ; D is the rainfall duration in hours.

[0121] (2) Soil-rock dual translation landslide

[0122] When the residual slope soil layer overlying the bedrock is thin, under the action of rainfall, river erosion and surface drainage, water smoothly infiltrates into the interface between the residual slope layer and the soil layer along the cracks, and accumulates on the top of the sandstone bedrock to form a muddy interlayer, which causes the shear strength of the interface to drop sharply, and the overlying residual slope soil layer slides, deforms and destroys along the top of the underlying bedrock. This is a parallel landslide of soil and rock. The rainfall water during the concentrated rainfall period may continue to penetrate deep into the overburden of the slope, and the shear strength and deformation parameters of the overburden and fully weathered rock on the slope will gradually decrease as the rock and soil become saturated, which will lead to a continuous decrease in the stability of the slope. Studying the failure mechanism of the binary slope under water infiltration is helpful for subsequent monitoring and early warning research of the slope. The failure mechanism of the binary slope under water infiltration was analyzed by numerical simulation and limit equilibrium method.

[0123] In the simulation calculation of soil-rock binary translation landslide, the slope section at K88+236~K88+400 (right) is selected as an example. The surface covering layer is about 1~2.5 meters thick and is silty clay; the underlying strongly weathered marl is soft and broken. The model is 137m long and 73m high. Considering excavation, the net height of the slope is 61m, of which the overlying soil is silty clay with a thickness of 2.5m.

[0124] For soil-rock binary translation landslide, it is divided into a binary slope with a gentle contact surface and a steep contact surface. For the binary slope with a gentle contact surface, 10° is taken in this paper, and for the steep contact surface slope, 45° is taken. By controlling the water content of the slope silt layer and the fully weathered rock layer to gradually increase from the surface to the inside to simulate the water infiltration process, the analysis conditions shown in Table 9 were established.

[0125] Table 9 Calculation conditions of two-dimensional slope with gently inclined contact surface

[0126]

[0127] For the steep and inclined binary slope, in order to simulate the water infiltration process, the water content of the silty clay layer and the weathered sandstone layer of the slope is gradually increased from the surface to the inside to simulate the water infiltration process, and the analysis conditions shown in Table 10 are established.

[0128] Table 10 Calculation conditions of steep slope with contact surface

[0129]

[0130] In the numerical simulation, the slope strike width was taken as 1 m and the displacement of the slope strike was restricted to simulate the plane strain analysis. The normal displacements of the left, right and bottom of the slope model were restricted. The constitutive model of silt and fully weathered rock adopted the Strainsoftening constitutive model, and the constitutive model of moderately weathered rock adopted the Mohr-Colum constitutive model. The calculation termination condition was that the ratio of the average unbalanced force of all model nodes to the average force acting on all nodes reached 1.1×10 -4 In the analysis of different working conditions, the property parameters of silty clay and weathered sandstone at different moisture contents are obtained from the above indoor geotechnical tests. In the limit analysis software of numerical analysis, when the sliding surface is in the shape of an arc, the simplified Bishop method can be used to calculate the slope stability coefficient; when the sliding surface is in the shape of a broken line, the transfer coefficient method and the Morgenstern-Price method can be used to calculate the slope stability coefficient, and the minimum value of the slope stability coefficient calculated by the two methods is taken.

[0131] After numerical simulation, the following results are obtained:

[0132] 2.1 Failure mechanism of dual slope with gently inclined contact surface

[0133] The plastic zone identification diagram under the typical working condition of the gently inclined contact surface binary slope was obtained through analysis. The plastic zone identification can be used to analyze the tensile and shear failure mechanisms of the slope. Tension-n or shear-n means that the model unit area is in the critical state of the tensile or shear plastic zone, and tension-p or shear-p means that the model unit area was once in the critical state of the tensile or shear plastic zone. Under working condition 1, the moisture content of silty clay and weathered sandstone is 18%, and a tension plastic zone appears in the shallow silt layer on the top surface of the slope near the right boundary, and a shear plastic zone develops inside the fully weathered rock layer in the middle front part near the free surface of the slope. The slope stability coefficient is 1.374; Under working condition 4, the moisture content of silty clay and weathered sandstone is 20%, and the tension plastic zone generated in the shallow silt layer on the top surface of the slope near the right boundary is still developing and showing a trend of extending toward the slope shoulder. A shear plastic zone with a smaller width appears in the upper silt layer of the fully weathered rock layer in the middle front part near the free surface of the slope. The shear plastic zone has a straight front edge in appearance. The front edge of the slope is straight and the rear edge is arc-shaped, and the slope stability coefficient is 1.116; under working condition 5, the moisture content of silty clay is 23.5%, and the moisture content of weathered sandstone is 18%. The tensile plastic zone generated in the shallow silt layer on the top surface of the slope near the right boundary has extended to the shallow silty clay layer on the top surface of the slope with a horizontal distance range of 0 to 1.1h from the shoulder point (h is the vertical distance between the outcropping point of the binary slope soil-rock contact surface on the slope surface and the shoulder point). A shear plastic zone with a relatively wide width appears in the middle and front part near the free surface of the slope. The overall appearance of the connected shear plastic zone and tensile plastic zone shows that the front edge is straight and the rear edge is arc-shaped, and the slope stability coefficient is less than 1.0. As water migrates into the silty clay and weathered rock layers of the binary slope with a gently inclined contact surface, the shear strength gradually decreases, resulting in the appearance of a tensile plastic zone in the shallow silty clay at the top of the slope and a shear plastic zone in the middle front, until the shear plastic zone and the tensile plastic zone form a through composite sliding surface, causing the slope to become unstable (the stability coefficient is less than 1). In addition, due to the migration of water into the silty clay and weathered rock layers of the binary slope with a gently inclined contact surface, the binary slope body near the free surface undergoes significant deformation toward the free surface, which in turn causes the tensile plastic zone on the top of the slope to gradually develop into the silty clay layer on the top of the slope near the shoulder. The appearance of a tensile plastic zone on the top of the slope indicates that tensile cracks will appear on the top of the slope, causing rainfall in the rainy season to further infiltrate into the slope body along the tensile cracks, thereby promoting the rapid development of slope instability.

[0134] The sliding surface determined by numerical simulation and limit equilibrium analysis of the binary slope with gentle contact surface under different working conditions was obtained by simulation. The maximum shear strain zone of the numerical simulation analysis represents the sliding surface of the slope. As the water migrates into the silty clay and weathered sandstone layers of the binary slope with gentle contact surface, the sliding surface that gradually tends to be connected in the numerical simulation model eventually develops into a composite sliding surface composed of a straight line segment in the front weathered sandstone layer and an arc segment in the rear silt layer. This composite sliding surface can be approximately replaced by the arc sliding surface determined by the limit equilibrium analysis method, and the position of the sliding exit is in the fully weathered rock. The horizontal distance between the intersection of the straight line segment and the arc segment of the composite sliding surface of the slope and the exposed point of the soil-rock contact surface on the slope is about 2h / 3, and the horizontal distance between the intersection of the arc segment of the composite sliding surface and the top surface of the slope and the slope shoulder is about 1h.

[0135] Figure 4 The curves of the stability coefficient of the two-dimensional slope with a gentle contact surface and the analysis conditions are summarized in the paper. It can be seen that with the infiltration of water into the silt and fully weathered rock, the slope stability coefficient decreases significantly. Figure 4 From the perspective of water infiltration, the internal boundary of the silty clay layer that affects the stability of the slope is about 0.35h away from the comprehensive slope line.

[0136] 2.2 Failure mechanism of steep and inclined contact surface dual slope

[0137] The simulation analysis obtained the plastic zone identification diagram under the typical working condition of the steep and inclined contact surface binary slope, which is closer to the actual situation on site. Under working condition 1, the mass moisture content of the silty clay layer is 20%, and the mass moisture content of the weathered sandstone layer is 18%. A tensile plastic zone appears in the shallow silt layer from the intersection of the soil-rock contact surface and the top surface of the slope to the right boundary of the model, and a shear plastic zone develops inside the fully weathered rock layer in the steep section and the bottom horizontal section. The slope stability coefficient is 1.328; Under working condition 2, the mass moisture content of the silty clay layer and the weathered sandstone layer is 20%, and an obvious tensile plastic zone appears in the shallow silt layer near the intersection of the soil-rock contact surface and the top surface of the slope. The shear plastic zone develops further inside the fully weathered rock layer in the steep section and the bottom horizontal section, and the slope stability coefficient is 1.175; Under working condition 3, the mass moisture content of the silty clay layer is 22%, and the mass moisture content of the weathered sandstone layer is 18%. The mass moisture content is 20%. The area of ​​the tensile plastic zone in the shallow silt layer near the intersection of the soil-rock contact surface and the top surface of the slope increases. In addition to the shear plastic zone in the weathered sandstone layer in the steep section and the bottom horizontal section, a small-scale arc-shaped shear plastic zone appears in the silt layer near the foot of the slope. No through sliding surface is formed between the tensile plastic zone and the shear plastic zone. The slope stability coefficient is 1.074. Under working condition 4, the mass moisture content of the silty clay layer and the weathered sandstone layer is 22%. A tensile plastic zone appears in the shallow silt layer from the intersection of the soil-rock contact surface and the top surface of the slope to the shoulder point. In addition to the shear plastic zone in the fully weathered rock layer in the steep section and the bottom horizontal section, a large-scale arc-shaped shear plastic zone appears in the silty clay layer. A through sliding surface is formed between the tensile plastic zone and the shear plastic zone. The slope stability coefficient is 0.992. As water migrates into the steep dip contact type binary slope, the shear strength of the silty clay layer and the weathered sandstone layer gradually decreases. First, a tensile plastic zone appears in the shallow silty soil layer near the intersection of the soil-rock contact surface and the top surface of the slope, and a shear plastic zone develops in the fully weathered rock layer in the steep section and the bottom horizontal section, until the shear plastic zone and the tensile plastic zone in the silty clay layer form a continuous arc-shaped sliding surface, causing the slope to become unstable (the stability coefficient is less than 1). In addition, due to the migration of water into the steep dip contact type binary slope, the binary slope body near the free surface has a significant deformation toward the free surface, which causes the tensile plastic zone in the shallow soil layer near the intersection of the soil-rock contact surface and the top surface of the slope to gradually develop into the top layer of the slope near the slope shoulder. The appearance of tensile plastic zone on the top surface of the slope indicates that tensile cracks will appear on the top of the slope, causing rainfall in the rainy season to further infiltrate into the slope along the tensile cracks, thereby promoting the rapid development of slope instability and failure.

[0138] At the same time, the sliding surface determined by numerical simulation and limit equilibrium analysis of the steep down-dipping contact surface binary slope under typical working conditions is obtained. As water migrates into the silt layer and fully weathered rock layer of the steep down-dipping contact surface binary slope, although a non-penetrating sliding surface first appears in the fully weathered rock of the steep section, a penetrating arc-shaped sliding surface is finally formed in the silt, and the position of the sliding exit is at the contact surface between the silt and the fully weathered rock; the horizontal distance between the intersection of the slope penetrating sliding surface and the slope top surface and the slope shoulder is about 0.26h. For the steep down-dipping contact surface binary slope, its penetrating arc-shaped sliding surface appears in the silt layer, which may be related to the fact that the fully weathered layer is far away from the comprehensive slope surface of the slope. When the fully weathered layer is close to the comprehensive slope surface of the slope, combined with the results of the numerical simulation sliding surface of the steep down-dipping contact surface binary slope under typical working conditions, it can be inferred that the shape of the slope sliding surface will be arc-shaped at the bottom and a straight line segment along the fully weathered layer at the top.

[0139] Figure 5 The curve of the change of the stability coefficient of the steep contact surface binary slope with the analysis conditions is compiled. It can be seen that: with the infiltration of water into the silty clay and weathered sandstone, the slope stability coefficient continues to decrease. Under the condition of water infiltration, the internal boundary of the sensitive silty clay layer that affects the stability of the slope is about 0.4h away from the comprehensive slope line.

[0140] 2.3 Effect of slope gradient and overburden thickness on slope stability

[0141] In addition, in order to analyze the influence of different overburden thickness on the stability of soil-rock dual structure slope, eight overburden thicknesses were selected, including 2.5m, 3.0m, 3.5m, 4.0m, 4.5m, 5.0m, 5.5m and 6.0m, and six slope angles of 20°, 25°, 30°, 35°, 40° and 45° were selected for calculation. The calculation results of the stability of the dual structure slope are shown in the figure. Figure 6 shown.

[0142] Under the same slope conditions, the safety factor of the slope gradually decreases with the increase of the thickness of the overburden, and the stability of the slope gradually decreases. When the slope is 10°, the thickness of the overburden is between 2.5 and 6m, and the slope safety factor is greater than the specified stability safety factor of 1.0. At this time, the slope is basically stable. Under the same overburden thickness conditions, the safety factor of the slope gradually decreases with the increase of the slope, the stability of the slope gradually decreases, and the possibility of landslide increases accordingly.

[0143] When the thickness of the overburden is 2.5m and the slope is 10°, the safety factor of the slope is greater than 1.0, and the slope is basically stable; when the slope is 45°, the safety factor of the slope is less than 1.0, and the slope is unstable and needs to be reinforced. When the thickness of the overburden is 3m, the slope stability and instability boundary slope drops to 30°. When the thickness of the slope soil increases to 4m and above, most slopes are unstable and need to be reinforced in time. Therefore, it is recommended that the thickness of the overburden should not exceed 4m, and reinforcement is required if it exceeds 4m.

[0144] 2.4 Effect of soil mechanical properties on slope safety factor

[0145] Figure 4 .30 is a curve diagram of simulated safety factor of slope with different internal friction angles. Figure 7 It can be seen that when the cohesion of the overlying soil layer is the same, as the internal friction angle increases, the safety factor of the slope gradually increases, and the stability of the slope gradually improves. When the cohesion is 10kPa and the internal friction angle increases to 25°, the maximum safety factor is 1.10, which does not meet the stability safety factor requirements of general slopes specified in the specifications. Therefore, the soil cohesion is 10kPa, which does not meet the requirements for slope stability. When the internal friction angle of the overlying soil layer is the same, as the cohesion increases, the safety factor of the slope gradually increases, and the stability of the slope gradually improves.

[0146] 2.5 Effect of rainfall conditions on slope safety factor

[0147] Figure 8 The curve diagram of the simulated safety factor of the slope under different rainfall conditions. It can be seen that with the increase of rainfall infiltration depth, the safety factor of the slope gradually decreases, and the stability of the slope gradually decreases. When the rainfall infiltration depth is 0.5m, the maximum safety factor of the slope is 1.4; when the rainfall infiltration depth increases to 5m, the safety factor of the slope drops to 0.8.

[0148] (3) Rock layer landslide

[0149] Firstly, the Hoek-Brown failure criterion is integrated into the principle derivation of the Morgenstern-Price method to achieve accurate judgment of rock slope engineering. To calculate the shear strength-normal stress curve, four parameters are required, which are as follows: σ ci : Uniaxial compressive strength of rock block; m i : rock mass properties; GSI: geological strength index (0-100); D: rock mass disturbance factor (0-1).

[0150] Using D, GSI, σ ci and m i Calculate m b The formula is as follows:

[0151]

[0152] The curve parameters α and s are calculated by the following formula:

[0153]

[0154] The GSI of the original rock is 100, and s is 1.0. In the early failure criteria, the parameter α was assumed to be a constant of 0.5. It is now considered to be a variable related to GSI.

[0155] At failure, the relationship between the principal stresses is:

[0156] The intensity curve is established by calculating σ1 through a series of given σ3.

[0157] The default range of σ3 is from the rock tensile strength value (negative value) to half of the uniaxial compressive strength value. The tensile strength is calculated as follows:

[0158]

[0159] Get the σ1-σ3 value at the time of destruction, τ-σ n The data points can be calculated like this:

[0160]

[0161] The software calculates the normal stress on the bottom of each strip, finds the slope of the spline curve, and uses it as the internal friction angle of the material. The tangent of the curve is extended to the τ axis, and the intercept is set as the cohesion. In this way, each strip has a different c, The value is substituted into the MP method to calculate the slope safety factor.

[0162] In the initial state simulation calculation, the calculation model considers 2 factors with 4 levels each. After completing the simulation calculation of a total of 16 models, variance analysis is performed. The slope height and slope of the initial state are shown in Table 11. For material selection, the upper layer of the rock slope is selected as strongly weathered sandstone, and the lower layer is weakly weathered sandstone. The material model is the Mohr-Coulomb model and the elastoplastic model, and the yield criterion adopts the Mohr-Coulomb criterion. The slope engineering stress-strain calculation parameters are shown in Table 12.

[0163] Table 11 Influencing factors and level selection

[0164] level 1 2 3 4 high 20 30 40 50 slope 1:0.8 1:1 1:1.2 1:1.4

[0165] Table 12 Calculation parameters of soil properties for slope engineering

[0166]

[0167] When simulating the calculation of different influencing factors, the slope calculation model is constructed based on the slope section at LK3+260. The model is 165m long and 72m high. Considering excavation, the net height of the slope is 47m. The slope construction form and anchoring structure have been described in the previous article. The calculation model is shown in Figure 4 .34, a total of 2315 nodes, 2245 units, and 5 feature points.

[0168] In the geostress and simulation conditions, the mechanical response of the cutting slope under long-term action is first calculated, and the stress value of each point is extracted after its deformation is stabilized. The extracted stress value is used as the initial stress input of the geostress balance of the slope model, and the model after geostress balance is loaded as the initial state of the slope model. Different construction intervals, that is, the interval time after the completion of each level of slope construction and the slope stability with / without anchoring structure are calculated respectively. The construction intervals are 3d, 5d, and 8d respectively, and the anchoring effect is divided into with / without anchoring. The 5d interval and with anchoring in the actual construction process are taken as the standard conditions.

[0169] 3.1 Correlation between initial state and slope stability

[0170] The slope safety factors under 16 initial working conditions are obtained through numerical calculation, and the calculation results are shown in Table 13.

[0171] Table 13 Rock slope stability under geometric factors

[0172]

[0173] The analysis shows that the safety factor of the rock slope is negatively correlated with the slope height and positively correlated with the slope ratio. When the slope ratio is constant, the safety factor of the rock slope decreases with the increase of the slope height, and the decreasing trend of different slope ratios is relatively close. According to the Pearson correlation analysis, the correlation between the safety factor and the slope height is -0.89; when the slope height is constant, the safety factor of the rock slope increases with the increase of the slope ratio. When the slope height is low, this trend is more obvious, and the correlation between the safety factor and the slope ratio is 0.41. The rock slope is significantly affected by the slope height, but weakly affected by the slope ratio, which is consistent with the material characteristics of the rock slope.

[0174] 3.2 Slope deformation law under excavation unloading

[0175] As the construction excavation progressed, the slope showed an obvious "stress release" phenomenon. In both the X and Y directions, the displacement showed a trend of deviating from the slope. Among them, the X-direction displacement showed an inward development trend in the early stage. The displacement of the characteristic point 1 with the largest deformation (i.e. the slope vertex) was about 2mm. After the excavation of the third-level slope, the displacement direction showed an obvious trend of deviating from the slope. The displacement increased from top to bottom, ranging from 1.06 to 4.65mm. The cumulative deformation of the slope under standard working conditions was Fig. 9 .

[0176] With the relief of stress release and the change of slope structure, the displacement in the Y direction changes from uplift to settlement. The deformation increases with the increase of excavation depth, and the maximum uplift value is between 2.67 and 11 mm. It is worth noting that the time point of the maximum uplift of each level of slope is different. The higher the uplift, the earlier it appears and the earlier it enters the decline range. In general, with the progress of construction, the road cutting excavation transitions from a relatively loose strongly weathered layer to a complete rock layer with high ground stress, the stress release is significantly enhanced, and the displacement development trend of the deviated slope begins to become prominent. However, the deformation mechanism in the X and Y directions is not completely consistent, and the deformation process is not highly correlated, which needs to be analyzed in combination with specific circumstances.

[0177] The displacement in the X direction in the displacement cloud map is mainly concentrated in the middle of the 3rd level slope to the middle of the 5th level slope. Affected by the superposition of excavation unloading and stress release, the maximum change is about 6mm; the displacement in the Y direction is also mainly concentrated in the above area, but the distribution along the height direction is more uniform, with a maximum change of about 11mm. It is generally believed that during the construction of the road cut slope, special attention should be paid to the deformation state of the middle and lower areas, especially during the excavation of the complete rock layer, and local spalling of the rock slope caused by large deformation should be prevented.

[0178] 3.3 Analysis of overall slope stability

[0179] The rock mass of the slope is intact and the slope is relatively gentle. Its overall stability is good and the risk of overall landslide is not high. Fig.10 , with the deepening of slope excavation, it dropped from 2.66 to 1.47, with a significant drop. The largest drop occurred in the excavation process of the third-level slope, which is consistent with the intensified stress release phenomenon in this area analyzed previously. Although the minimum safety factor of 1.47 is relatively reliable, it was found during the calculation process that shallow surface landslides occurred in the medium-weathered rock layer, and this phenomenon should be paid attention to during the construction of this type of slope.

[0180] 3.4 Comparison of reinforcement effects with and without anchoring

[0181] Maximum vector displacement see Fig.11 , its change trend is similar to the above, but the presence or absence of anchorage has a greater impact on the slope deformation. Compared with 13.38mm without support, the anchor structure can reduce the deformation by 16.6%, down to 11.15mm. The analysis shows that the anchor structure has a significant effect on restricting the deformation of rock slopes, and should be strengthened in the construction process of high-risk slopes.

[0182] Safety factor with / without anchorage Fig.12, the two showed a big difference, and this difference gradually increased with the progress of the excavation process. After the last level of slope construction was completed, the slope safety factor with anchoring was 1.47, which was 32% higher than 1.11 without support. The analysis shows that anchoring support structures can play a significant role in improving the overall stability of rock slopes.

[0183] Example 2

[0184] This embodiment also provides an electronic device, including at least one processor, a memory connected to the at least one processor, and at least one input / output interface connected to the at least one processor; the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute a slope instability mechanism analysis method of the aforementioned embodiment. The input / output interface may include a display, a keyboard, a mouse, and a USB interface for inputting and outputting data.

[0185] The electronic device can be an electronic device for a client, such as a mobile phone, a laptop computer, a tablet computer, a desktop computer, etc., to execute a slope instability mechanism analysis method of Example 1.

[0186] Those skilled in the art can understand that: all or part of the steps of implementing the above-mentioned method embodiment can be completed by hardware related to program instructions, and the aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it executes the steps of the above-mentioned method embodiment; and the aforementioned storage medium includes: mobile storage devices, read-only memories (ROM), disks or optical disks, etc. Various media that can store program codes.

[0187] For those skilled in the art, when understanding the solutions described in the specific embodiments of the present invention, they can refer to the conventional technical manuals in the field. At the same time, for the places where the above-mentioned terms appear, they can make appropriate understandings or adjustments for reference, and deduce the implementation of the same or similar technical solutions without paying any creative work.

[0188] The above embodiments describe only the basic principles, main features and / or advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and the invention content of the specification only describe the principles or specific cases of the present invention. Without departing from the essence of the innovative idea of ​​the present invention, the innovative scheme of the present invention may be subject to various changes and improvements, and these changes and improvements all fall within the scope of protection required by the present invention.

Claims

1. A method for analyzing the mechanism of slope instability, characterized in that: The following steps are involved: Conduct investigation on the slope to be studied to determine the geological environment characteristics and the types of slope disasters; According to the geological environment characteristics of the slope and the types of slope damage disasters, the physical and mechanical properties of the slope soil are studied; Establish a slope calculation model, and simulate the influence of different slope heights and slope ratios on slope stability under the initial state through finite element numerical calculation, combined with the slope calculation model and the physical and mechanical properties data of the slope soil; The external factors that cause slope instability are analyzed. Through finite element numerical calculation, combined with the slope calculation model and the physical and mechanical properties of the slope soil, the stability and instability mechanism of the slope under different external factors are simulated and analyzed.

2. The method for analyzing the slope instability mechanism according to claim 1 is characterized in that: The geological environment characteristics of the slope and the types of slope disaster damage are determined through domestic and foreign literature and on-site investigations. The geological environment characteristics of the slope include topography, stratum lithology, climate environment, and seismic activity; the types of slope disaster damage include deformation, cracking, and landslide.

3. The method for analyzing the slope instability mechanism according to claim 1, characterized in that: The method for studying the physical and mechanical properties of slope soil is: select soil on the slope to carry out indoor geotechnical tests on particle grading, critical moisture content, and natural bulk density, and study the basic physical properties, soil-water properties, permeability properties, and shear strength properties of soils with different degrees of weathering. The basic physical properties include moisture characteristics, density characteristics, and particle size characteristics. The soil-water properties and permeability characteristics include soil-water characteristic curves and unsaturated permeability coefficients. The shear strength characteristics include internal friction angles and cohesion.

4. The method for analyzing the slope instability mechanism according to claim 3 is characterized in that: When calculating the unsaturated permeability coefficient, based on the constant head permeability test, the saturated permeability coefficient of soil-rock mixture with different stone contents was measured. Combined with the soil-water characteristic curve of the soil, the Van Genuchten model was used to fit the model parameters, so as to calculate the unsaturated permeability coefficient of the slope soil with different stone contents.

5. The method for analyzing the slope instability mechanism according to claim 1, characterized in that: The method for simulating the influence of different slope heights and slope ratios on slope stability under the initial state is as follows: numerical calculation is performed based on the unsaturated shear strength failure criterion related to matrix suction. Specifically, the suction level of each unit in the slope calculation model is determined according to the current suction field of the embankment, and the equivalent cohesion including suction is calculated; Then the current stress state is determined and the shear strength contribution of the effective normal stress is calculated; Determine whether instability failure occurs at the current shear strength level; If instability does not occur, further reduce the strength; If instability occurs, the reduction is judged to be complete, and the position of the most dangerous sliding surface and the safety factor are determined.

6. The method for analyzing the slope instability mechanism according to any one of claims 1 to 5, characterized in that: Slope damage disaster types include landslides. According to the morphological characteristics and mechanisms of landslides, landslides include rock bedding landslides, residual slope accumulation soil landslides, and soil-rock binary translation landslides.

7. The method for analyzing the slope instability mechanism according to claim 6, characterized in that: For residual slope accumulation landslides, when rainfall infiltrates, the unsaturated soil mechanics stability analysis method of the slope is as follows: set the embankment soil permeability parameters, the relationship between the suction parameters and the humidity parameters, the seepage rules, the infiltration boundary conditions and the rainfall type, determine the initial humidity field and the suction field, calculate the transient humidity field and the suction field, determine the transient suction level of each unit, calculate the effective cohesion, calculate the embankment stress level, calculate the embankment shear strain or the characteristic point displacement, and then determine whether the instability judgment standard is met. If not, adjust the reduction factor and return to recalculate the effective cohesion. If it is met, determine the position of the most dangerous sliding surface and determine the safety factor.

8. The method for analyzing the slope instability mechanism according to claim 6, characterized in that: For soil-rock binary translation landslide, numerical simulation and limit equilibrium method are used to analyze the failure mechanism of binary slope under water infiltration when simulating and analyzing the stability and instability mechanism of slope under different external influencing factors. In the numerical simulation of soil-rock binary translation landslide, the slope strike width is taken as 1m and the displacement of the slope strike is restricted to simulate plane strain analysis. The normal displacements of the left, right and bottom of the slope model are restricted. The constitutive model of silt and fully weathered rock adopts the Strainsoftening constitutive model, and the constitutive model of moderately weathered rock adopts the Mohr-Colum constitutive model. The calculation termination condition is that the ratio of the average unbalanced force of all model nodes to the average force acting on all nodes reaches 1.1×10 -4 ; When the sliding surface is in the shape of an arc, the simplified Bishop method is used to calculate the slope stability coefficient; when the sliding surface is in the shape of a broken line, the transfer coefficient method and the Morgenstern-Price method are used to calculate the slope stability coefficient, and the minimum value of the slope stability coefficient calculated by the two methods is taken.

9. The method for analyzing the slope instability mechanism according to claim 6, characterized in that: For rock bedding landslides, the Hoek-Brown failure criterion is integrated into the principle derivation of the Morgenstern-Price method during the numerical simulation process to calculate the slope safety factor.

10. An electronic device comprising at least one processor and a memory in communication with the at least one processor; the memory stores instructions executed by the at least one processor, characterized in that: The instructions are executed by the at least one processor so that the at least one processor can execute the slope instability mechanism analysis method described in any one of claims 1-9.

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