Fracture slope stability evaluation method considering spatial distribution non-uniformity of rock-soil body

Abstract

The invention discloses a crack slope stability evaluation method considering spatial distribution nonuniformity of a rock-soil body, and the method comprises the steps: determining a minimum enclosing rectangle according to the size of a to-be-modeled slope model, and generating a tensile strength random field; based on a fracture random expansion algorithm, generating a random fracture model in a minimum bounding rectangle range; covering the fracture model into the slope model area to generate a fracture slope model; importing the fracture slope model and the parameter random field into finite element calculation software, dividing grids and setting boundary conditions and load steps; and calculating by adopting a strength reduction method to obtain a failure mode and a safety coefficient of the fractured slope. According to the method, the random field theory, the fracture random expansion algorithm and the slope stability evaluation method are combined, the spatial distribution nonuniformity of the rock-soil body under the natural condition is fully considered, and the problem that in a traditional fracture slope model, the fracture form is simplified through manual hand drawing or random cross straight lines is solved; and the authenticity of fracture slope modeling and calculation results is improved.

Description

Technical Field

[0001] The invention relates to the technical field of fracture slope stability analysis, and in particular to a fracture slope stability evaluation method taking into account the spatial uneven distribution of rock and soil bodies. Background Art

[0002] The stability of the slope is directly related to the safety and economic benefits of the project. Due to the complexity of the geological environment and the uneven spatial distribution of rock and soil, slope instability problems occur from time to time, which brings great challenges to engineering construction. Fracture slopes are widely present in rock or soil slopes in nature, and their development degree and spatial distribution characteristics have a significant impact on the mechanical properties and stability of the slope. At present, the main methods for slope stability evaluation include limit equilibrium method, finite element method, discrete element method, etc. These methods have achieved certain results in slope stability analysis, but there are still great limitations in the characterization of the spatial uneven distribution of rock and soil and the modeling and calculation of fractured slopes. The local instability of the slope caused by the development of local fractures or local loose accumulation is difficult to accurately calculate by the existing analysis and calculation methods. Therefore, how to simulate the spatial variability of rock and soil parameters in the slope, characterize the true form of the fracture, and perform stability calculation is a problem that needs to be solved urgently. Summary of the invention

[0003] The purpose of the present invention is to provide a fracture slope stability analysis method which can take into account the spatial distribution heterogeneity of rock and soil in its natural state and can simulate the real fracture morphology in order to overcome the shortcomings of the existing methods.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A method for evaluating the stability of a fractured slope taking into account the spatial non-uniform distribution of rock and soil mass, characterized in that it comprises the following steps:

[0006] Step 1: According to the actual situation of the slope, determine the maximum width and depth of the structural fissures in the slope, and determine the length L of its minimum circumscribed rectangle according to the range of the fissures to be generated. r and width W r , the rectangular area is the crack simulation area;

[0007] Step 2: Divide the crack simulation area into grids. The grid form is regular triangle, and the grid side length is l t ;

[0008] Step 3: Generate the tensile strength s of the rock mass in the fracture simulation area t The random field of is used to quantitatively characterize the spatial variability of parameters caused by the uneven spatial distribution of rock and soil mass; it includes the following sub-steps:

[0009] Step 3-1: Considering the non-negativity of soil parameters, the marginal distribution of the random field adopts the gamma distribution, and the mean μ and coefficient of variation c of the gamma distribution are selected according to the actual situation of the slope. v and the horizontal and vertical correlation lengths SOF x 、SOF y ;

[0010] Step 3-2: Generate a random field in the simulation area using the spectral decomposition method according to the selected parameters, and assign it to the grid nodes. The parameters include the mean μ of the gamma distribution, the coefficient of variation c v and the horizontal and vertical correlation lengths SOF x , SOF;

[0011] Step 4. Set the global tensile stress σ of the site according to the actual situation of the slope t and stress release influence radius r s , if there is a lack of relevant data, set the tensile stress equal to the mean of the random field to obtain a better crack morphology;

[0012] Step 5: Determine the number of cracks n in the slope according to the actual situation of the slope c , average width w ac and the maximum length l mc ;

[0013] Step 6: generating an initial breaking point in the simulation area; including the following sub-steps:

[0014] Step 6-1, according to the random tensile strength values ​​at the mesh nodes, extract the mesh nodes whose tensile strength is less than the global tensile stress and sort them by tensile strength;

[0015] Step 6-2: Start the fracture from the mesh node with the smallest tensile strength, and take the fracture point as the center of the circle. s A stress relief influence zone is defined for the radius, in which another initial fracture point cannot be generated;

[0016] Step 6-3: Repeat step 6-2 until the number of initial breakpoints generated reaches n c Or there are no mesh nodes outside the stress relief zone whose tensile strength is lower than the global tensile stress;

[0017] Step 7: Perform iterative calculation based on the initial breakpoint, with the number of iteration steps being n. i , when the crack extends to the edge of the simulation area or the high tensile strength area, or reaches a predetermined number of iterations, the crack will stop developing;

[0018] Step 8: Import the coordinates of the slope contour nodes, i.e., the coordinates of the vertices of the regular triangle mesh on the slope contour, delete the mesh outside the contour, extract the edge contour, and export the model file format that can be used for numerical calculation; and import the model file into the finite element numerical calculation software;

[0019] Step 9: extract the coordinates of the equilateral triangle mesh vertices and the random tensile strength of the assigned coordinates of each equilateral triangle mesh vertex, set the internal friction angle to a constant value, and calculate the cohesion corresponding to each equilateral triangle mesh vertex through formula (1), which is expressed as:

[0020]

[0021] Where c is the cohesion, in kPa; s t is the tensile strength, in kPa; is the internal friction angle, in degrees.

[0022] Step 10: Generate an interpolation function based on the discrete cohesion data and import it into the finite element numerical calculation software, and assign values ​​to the slope area outside the crack based on the interpolation function and the fixed internal friction angle;

[0023] Step 11: assign parameters to the cracks according to the actual situation of the slope, divide the slope model into grids, and calculate by the strength reduction method;

[0024] Step 12: After the calculation is completed, extract the slope safety factor and sliding surface shape for stability evaluation.

[0025] Furthermore, in step 1, if it is intended to generate structural fractures in the entire slope area, the fracture simulation area is the minimum circumscribed rectangle of the slope model.

[0026] Furthermore, in step 3, the mean, coefficient of variation and correlation length of the edge distribution should be determined according to the statistical parameters of the actual site, and the value of the correlation length should be smaller than the side length of the simulation area.

[0027] Furthermore, in step 7, the calculation formula for the number of iteration steps is:

[0028] Furthermore, in step 7, the crack is formed by splitting the mesh vertices, and the equilateral triangle mesh at the center of the crack is split into two in the horizontal or vertical direction. The tensile strength values ​​of the six vertices around the center of the crack are weightedly calculated to determine the probability of the crack tip developing in each direction.

[0029] Furthermore, in step 8, an edge detection algorithm is used to identify the boundaries of the crack and slope model and extract the edge contour.

[0030] Furthermore, in step 8, the algorithm selected to identify the boundaries of the crack and slope model and extract the edge contour should meet the four requirements of graphics denoising, edge detection, shape simplification and model export.

[0031] Furthermore, in step 11, in order to avoid the non-convergence problem of finite element calculation caused by the complex shape of the crack, the material should be assigned to the crack area; if the crack is considered to be a weak interlayer, the material parameters of the weak zone are assigned to the crack area; if the crack is considered to be a cavity, the cohesion is assigned to 0.001 kPa and the internal friction angle is assigned to 0°.

[0032] Furthermore, in step 11, considering that the density of the mesh inside the crack is very high and the crack distribution is the main factor affecting the shape of the sliding surface of the crack slope, in order to improve the calculation efficiency, the mesh of the non-crack slope area does not need to be refined.

[0033] The present invention realizes the acquisition of the failure mode of the fracture slope and the calculation of the safety factor by combining the random field theory, the crack random expansion algorithm and the finite element numerical calculation method. The method determines its minimum circumscribed rectangle according to the size of the slope model to be modeled; generates a tensile strength random field in the rectangular area; based on the crack random expansion algorithm, generates a random fracture model within the above minimum circumscribed rectangle by setting parameters such as the fracture length, width, number and global tensile stress; covers the fracture model to the slope model area to generate a fracture slope model; imports the fracture slope model and the parameter random field into the finite element calculation software, divides the grid and sets the boundary conditions and load steps; uses the strength reduction method to calculate and obtain the failure mode and safety factor of the fracture slope. The present invention fully considers the spatial distribution unevenness of the rock and soil under natural conditions by combining the random field theory, the crack random expansion algorithm and the slope stability evaluation method, overcomes the problem of simplifying the fracture morphology by hand-drawing or random cross straight lines in the traditional fracture slope model, and improves the authenticity of the fracture slope modeling and calculation results.

[0034] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The method of the present invention can take into account the spatial variability of rock and soil in its natural state;

[0036] (2) The method of the present invention can model a fracture slope with a real fracture morphology;

[0037] (3) The present invention provides a meshing method and a parameter assignment method for finite element analysis of fractured slopes, thereby improving the efficiency and convergence of model calculations. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The present invention is a flow chart of the method for evaluating the stability of a fissure slope.

[0039] Figure 2 Generate an effect diagram for the crack model involved in the present invention.

[0040] Figure 3 This is a calculation effect diagram of the fracture slope stability involved in the present invention. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] In this embodiment, taking a common soil slope as an example, the specific values ​​of the following parameters are respectively preferred parameters for evaluating a slope with a similar actual situation to the slope using the present invention.

[0043] like Figure 1 As shown in FIG. 1 , the fracture slope stability evaluation method based on the fracture random expansion algorithm includes the following steps:

[0044] (1) For the slope of this embodiment, the length L of the minimum circumscribed rectangle of the crack range to be generated is r and width W r Set to 15m and 6m respectively;

[0045] (2) Divide the fracture simulation area into grids. The grid form is an equilateral triangle with a grid side length of l t Set to 0.1m;

[0046] (3) Considering the non-negativity of soil parameters, the tensile strength of rock and soil s t The marginal distribution of the random field adopts the gamma distribution, and the mean μ of the gamma distribution is set to 10 kPa, and the coefficient of variation c v = 0.3, and the horizontal correlation length SOF x =8m, vertical correlation length SOF y =2m;

[0047] (4) Based on the selected parameters, the spectral decomposition method is used to generate the soil tensile strength s in the simulation area. t The random field is assigned to the grid nodes;

[0048] (5) Set the global tensile stress σ of the site t =10kPa, stress release influence radius r s =0.25m. If relevant data are lacking, the tensile stress can be set equal to the mean of the random field to obtain a better crack shape.

[0049] (6) Set the number of cracks n in the slope c =5, average width w ac =0.2m, maximum length lmc =20m;

[0050] (7) According to the random tensile strength values ​​at the nodes, the nodes whose tensile strength is less than the global tensile stress are extracted and sorted by tensile strength;

[0051] (8) Start to generate fracture from the node with the smallest tensile strength, and define the stress release influence area with the fracture point as the center and 0.25m as the radius. Another initial fracture point cannot be generated in this area. Repeat this process until the number of generated initial fracture points reaches 5 or there is no node outside the stress release area with a tensile strength lower than the global tensile stress;

[0052] (9) Iterative calculation is performed based on the initial point, with the number of iteration steps being 200. When the crack extends to the edge of the simulation area or reaches the predetermined number of iteration steps, the crack will stop developing. The crack model generation effect is shown in Figure 1. Figure 2 As shown;

[0053] (10) Importing the node coordinates of the slope contour, deleting the grid outside the contour, using the edge detection algorithm to identify the boundaries of the crack and slope model, extracting the edge contour, and exporting the model file format that can be used for numerical calculation; and importing the model file into the finite element numerical calculation software;

[0054] (11) Extract the node coordinates and the random tensile strength assigned to each coordinate. Set the internal friction angle to 20°. The cohesion c corresponding to each node can be calculated by formula (1) and expressed as:

[0055]

[0056] Where c is the cohesion, in kPa; s t is the tensile strength, in kPa; is the internal friction angle, in degrees.

[0057] (12) Generate an interpolation function based on the discrete cohesion data and import it into the finite element numerical calculation software. Based on this interpolation function and a fixed internal friction angle of 20°, assign values ​​to the slope area outside the crack;

[0058] (13) Assign parameters to the cracks according to the actual situation, divide the slope model into grids, and perform calculations using the strength reduction method;

[0059] (10) Figure 3 As shown in the figure, after the calculation is completed, the slope safety factor and the sliding surface shape are extracted, where the safety factor is 1.07.

[0060] It should be noted that the above embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present invention.

Claims

1. A fractured slope stability evaluation method considering the spatial heterogeneity of rock mass distribution, characterized in that: The following steps are involved: Step 1: According to the actual situation of the slope, determine the maximum width and depth of the structural fissures in the slope, and determine the length L of its minimum circumscribed rectangle according to the range of the fissures to be generated. r and width W r , the rectangular area is the crack simulation area; Step 2: Divide the crack simulation area into grids. The grid form is regular triangle, and the grid side length is l t ; Step 3: Generate the tensile strength s of the rock mass in the fracture simulation area t The random field of is used to quantitatively characterize the spatial variability of parameters caused by the uneven spatial distribution of rock and soil mass; It includes the following sub-steps: Step 3-1: Considering the non-negativity of soil parameters, the marginal distribution of the random field adopts the gamma distribution, and the mean μ and coefficient of variation c of the gamma distribution are selected according to the actual situation of the slope. v and the horizontal and vertical correlation lengths SOF x 、SOF y ; Step 3-2: Generate a random field in the simulation area using the spectral decomposition method according to the selected parameters, and assign it to the grid nodes. The parameters include the mean μ of the gamma distribution, the coefficient of variation c v and the horizontal and vertical correlation lengths SOF x , SOF; Step 4. Set the global tensile stress σ of the site according to the actual situation of the slope t and stress release influence radius r s , if there is a lack of relevant data, set the tensile stress equal to the mean of the random field to obtain a better crack morphology; Step 5: Determine the number of cracks n in the slope according to the actual situation of the slope c , average width w ac and the maximum length l mc ; Step 6: generating an initial breaking point in the simulation area; It includes the following sub-steps: Step 6-1, according to the random tensile strength values ​​at the mesh nodes, extract the mesh nodes whose tensile strength is less than the global tensile stress and sort them by tensile strength; Step 6-2: Start the fracture from the mesh node with the smallest tensile strength, and take the fracture point as the center of the circle. s A stress relief influence zone is defined for the radius, in which another initial fracture point cannot be generated; Step 6-3: Repeat step 6-2 until the number of initial breakpoints generated reaches n c Or there are no mesh nodes outside the stress relief zone whose tensile strength is lower than the global tensile stress; Step 7: Perform iterative calculation based on the initial breakpoint, with the number of iteration steps being n. i , when the crack extends to the edge of the simulation area or the high tensile strength area, or reaches a predetermined number of iterations, the crack will stop developing; Step 8: Import the coordinates of the slope contour nodes, i.e., the coordinates of the vertices of the regular triangle mesh on the slope contour, delete the mesh outside the contour, extract the edge contour, and export the model file format that can be used for numerical calculation; and import the model file into the finite element numerical calculation software; Step 9: extract the coordinates of the equilateral triangle mesh vertices and the random tensile strength of the assigned coordinates of each equilateral triangle mesh vertex, set the internal friction angle to a constant value, and calculate the cohesion corresponding to each equilateral triangle mesh vertex through formula (1), which is expressed as: Where c is the cohesion, in kPa; s t is the tensile strength, in kPa; is the internal friction angle, in degrees. Step 10: Generate an interpolation function based on the discrete cohesion data and import it into the finite element numerical calculation software, and assign values ​​to the slope area outside the crack based on the interpolation function and the fixed internal friction angle; Step 11: assign parameters to the cracks according to the actual situation of the slope, divide the slope model into grids, and calculate by the strength reduction method; Step 12: After the calculation is completed, extract the slope safety factor and sliding surface shape for stability evaluation.

2. The method for evaluating the stability of a fractured slope taking into account the spatial non-uniform distribution of rock and soil as claimed in claim 1, characterized in that: In step 1, if structural fractures are to be generated in the entire slope area, the fracture simulation area is the minimum circumscribed rectangle of the slope model.

3. The method for evaluating the stability of a fractured slope taking into account the spatial non-uniform distribution of rock and soil as claimed in claim 1, characterized in that: In step 3, the mean, coefficient of variation and correlation length of the marginal distribution should be determined according to the statistical parameters of the actual site, and the value of the correlation length should be smaller than the side length of the simulation area.

4. The method for evaluating the stability of a fractured slope taking into account the spatial non-uniform distribution of rock and soil as claimed in claim 1, characterized in that: In step 7, the calculation formula for the number of iterations is:

5. The method for evaluating the stability of a fractured slope taking into account the spatial non-uniform distribution of rock and soil mass as claimed in claim 1, characterized in that: In step 7, the crack is formed by splitting the mesh vertices. The regular triangle mesh at the center of the crack is split into two in the horizontal or vertical direction. The tensile strength values ​​of the six vertices around the center of the crack are weighted to determine the probability of the crack tip developing in each direction.

6. The method for evaluating the stability of a fractured slope taking into account the spatial non-uniform distribution of rock and soil mass as claimed in claim 1, characterized in that: In step 8, an edge detection algorithm is used to identify the boundaries of the crack and slope model and extract the edge contour.

7. The method for evaluating the stability of a fractured slope taking into account the spatial non-uniform distribution of rock and soil mass as claimed in claim 1, characterized in that: In step 8, the algorithm selected to identify the boundaries of the crack and slope model and extract the edge contour should meet the four requirements of graphics denoising, edge detection, shape simplification and model export.

8. The method for evaluating the stability of a fractured slope taking into account the spatial non-uniform distribution of rock and soil mass as claimed in claim 1, characterized in that: In step 11, in order to avoid the non-convergence problem of finite element calculation caused by the complex shape of the crack, the material should be assigned to the crack area; if the crack is considered to be a weak interlayer, the material parameters of the weak zone are assigned to the crack area; if the crack is considered to be a cavity, the cohesion is assigned to 0.001 kPa and the internal friction angle is assigned to 0°.

9. The method for evaluating the stability of a fractured slope taking into account the spatial non-uniform distribution of rock and soil mass as claimed in claim 1, characterized in that: In step 11, considering that the density of the mesh inside the crack is very high and the crack distribution is the main factor affecting the shape of the sliding surface of the crack slope, in order to improve the calculation efficiency, the mesh of the non-crack slope area does not need to be refined.

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