CN110598273A - Stability analysis method for non-saturated soil slope hydraulic mechanics coupling - Google Patents
Stability analysis method for non-saturated soil slope hydraulic mechanics coupling Download PDFInfo
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Abstract
The invention provides a stability analysis method for hydraulic mechanical coupling of an unsaturated soil slope, and belongs to the technical field of rock and soil. The method adopts a Baseline basic model which is more accordant with the properties of unsaturated soil for the constitutive model of the unsaturated soil, and considers the influence of suction force, the shearing strength and the compression strength of the soil body in the constitutive model. The intensity reduction method for analyzing the stability of the unsaturated soil slope reduces the shearing strength of the soil body by reducing the cohesive force and the friction angle of the soil body. In addition, the reduction of the compressive strength of the soil body is taken into account by reducing the front consolidation pressure of the soil body. The stability analysis of the unsaturated soil slope is carried out under a Cosserat continuum frame, and the influence of the microscopic structure effect of the soil body on the stability of the macroscopic slope is considered to a certain extent. The method considers various influence factors and improves the accuracy of the stability analysis of the unsaturated soil slope.
Description
Technical Field
The application relates to the technical field of rock and soil, in particular to a stability analysis method for coupling of unsaturated soil slope hydraulics.
Background
The mountain areas in China have extensive and large amounts of landslide disasters of unsaturated soil side slopes, and particularly the landslide disasters of the unsaturated soil side slopes are continuously generated along with the action of rainfall. In order to ensure the safety of engineering construction projects and the life and property safety of people, the research on the stability of unsaturated soil slopes is a considerable geological disaster research topic.
At present, the traditional method for researching the slope stability comprises the following steps: a limit balance method, a limit analysis method, a slip line field method, and the like. However, the methods do not consider the stress-strain relationship inside the soil body, are various stability analysis methods established on the basis of the extreme balance theory, cannot analyze the occurrence and development process of slope damage, simultaneously need to assume the shape and position of a slip fracture surface and the like to solve the safety coefficient, and are complex and not comprehensive in consideration.
And then, a finite difference method for slope stability analysis is adopted, wherein the finite difference method divides a solution domain into difference grids, and a continuous solution domain is replaced by a finite number of grid nodes. The strength reduction finite element method developed on the basis inherits the advantages of finite element calculation, can reasonably and comprehensively consider the constitutive relation of the soil body, does not need to assume the shape of a sliding surface, and can obtain the sliding surface which is most easy to slide through calculation. The method can reflect the non-uniformity of the slope soil body and the non-linearity of deformation and sliding, can obtain a potential sliding surface and a corresponding safety coefficient through calculation, and can simulate mechanical responses such as slope internal stress strain and the like.
In the related technology, the strength reduction finite element method is popularized to the analysis of the slope stability of unsaturated soil. The strength reduction method emphasizes the influence of the change of the suction force in the unsaturated soil on the shear strength of the unsaturated soil, thereby having important influence on the stability of the unsaturated soil slope. According to the intensity reduction method of the unsaturated soil slope, on the basis of the traditional intensity reduction method, a matrix suction item related to shear strength is reduced, and the contribution of the matrix suction to the slope stability is fully considered.
However, in the strength reduction method of the current slope stability analysis of unsaturated soil, the seepage of unsaturated soil is often simplified into a seepage model of saturated soil, and the coupling effect of the mechanical action of a solid skeleton and the seepage action of pore water and pore gas cannot be fully considered in the slope stability analysis. Moreover, the stability analysis of the unsaturated soil slope also often ignores the seepage effect of pore fluid of the slope, and does not consider the influence of the change of the suction field caused by the rainfall seepage effect on the slope stability in the used soil constitutive model.
In addition, when intensity reduction analysis is carried out, only the traditional soil mechanics constitutive model is adopted for reducing the shearing strength of the soil body of the side slope aiming at the unsaturated soil side slope, and the shearing strength and the compressive strength of the soil body are reduced simultaneously under the condition that the change of the soil body suction force is not fully considered. In addition, the intensity reduction method for analyzing the slope stability of the unsaturated soil is developed and applied on the basis of the traditional continuous medium mechanics, the consideration on the microscopic scale effect of the unsaturated soil is lacked, and the introduction of a regularization mechanism is lacked in the intensity reduction finite element simulation analysis of slope plastic slip. Therefore, the existing strength reduction method for analyzing the stability of the unsaturated soil slope has obvious defects, and the stability of the unsaturated soil slope cannot be accurately analyzed.
Disclosure of Invention
The embodiment of the invention provides a method for analyzing the stability of an unsaturated soil slope, aiming at improving the accuracy of the stability analysis of the unsaturated soil slope.
The application provides a stability analysis method for hydraulic mechanics coupling of an unsaturated soil slope, which comprises the following steps:
s100: and establishing a finite element numerical model of the side slope according to the geological model of the unsaturated soil side slope, physical and mechanical parameters of the soil body and hydraulic-mechanical load conditions.
S200: according to a Cosserat-Biot continuum finite element numerical simulation method of a Baseline basic model (BBM model) of unsaturated soil, an initial stress field and a pore fluid pressure field of a generated side slope under the action of gravity and rainfall are calculated, and an initial displacement field, a velocity field and a strain field of the side slope are reset.
S300: and setting a reasonable upper limit value and a reasonable lower limit value of the safety factor according to the initial requirement of the dichotomy of the slope safety factor solution.
S400: according to a Baseline basic model (BBM model) of unsaturated soil and a Cosserat-Biot continuum theory of solid, liquid and gas three-phase mechanics-seepage coupling, finite element calculation of intensity reduction method of slope stability analysis of unsaturated soil is carried out.
S500: and (4) performing dichotomy cyclic calculation of the intensity reduction method of the unsaturated soil slope stability analysis to obtain an analysis result.
In a specific embodiment, the calculation step of obtaining the analysis result by the dichotomy cycle calculation of the intensity reduction method of the unsaturated soil slope stability analysis comprises the following steps of
Determining the current reduction coefficient as the average value of the upper limit value and the lower limit value of the safety coefficient;
respectively reducing the cohesive force, the friction angle and the front consolidation pressure of the soil body;
and (4) carrying out hydraulic-mechanical finite element calculation of the side slope under the action of gravity and rainfall load by using the reduced soil body parameters, and judging the stability of the side slope by judging whether the calculation process is converged. If the calculation is convergent, the slope is stable, and if the calculation is not convergent, the slope is unstable;
if the side slope is stable, the lower limit value of the safety coefficient is expanded to be the current reduction coefficient, otherwise, if the side slope is unstable, the upper limit value of the safety coefficient is reduced to be the current reduction coefficient;
judging whether the difference between the upper and lower limit values of the safety coefficient meets the error requirement, if not, continuing the cyclic calculation of the dichotomy of the safety coefficient solution, and if so, jumping out of the iterative calculation;
after the error requirement of the safety coefficient is met, setting the average value of the upper limit value and the lower limit value of the current safety coefficient as the final slope stability safety coefficient, reducing the strength parameter of the slope soil body under the safety coefficient, and calculating to obtain the analysis results of the stress, the strain, the displacement, the pore water pressure, the suction force and the like of the slope in the critical instability state.
In a specific embodiment, the intensity reduction method for the unsaturated soil slope stability analysis implements the reduction of the shear strength of the soil body by reducing the cohesive force and the friction angle of the soil body, and also includes the reduction of the compressive strength of the soil body by reducing the front consolidation pressure of the soil body. This process comprises
Based on the correlation theory of the strength reduction finite element method of slope stability analysis, the reduction cohesive force and the friction angle are considered, and the reduction formula is
In the formulas 1 and 2, F is a reduction coefficient, c,Respectively cohesive force and friction angle, c'),Respectively the cohesive force and the friction angle after the folding.
The effect of suction is considered for the strength of unsaturated soil. Based on Fredlund's reduction of strength theory, the strength of the substrate suction s needs to be taken into account in the total effective cohesion, some
In the formula 3, c' is the cohesive force of the unsaturated soil after the reduction, and chi is a suction parameter.
Correspondingly, the effective shear strength of the unsaturated soil is reduced, and the reduced effective shear strength tau 'of the unsaturated soil is obtained'fCan be expressed as
As shown in formula 4, the relative cohesive force c and the friction angleThe reduction of the shear strength of the unsaturated soil is realized.
And (3) aiming at the BBM model of the unsaturated soil, reducing the front consolidation pressure strength of the unsaturated soil. To consolidation pressure before saturationPerforming reduction with the formula of
In formula 5The consolidation pressure before saturation after reduction.
According to the front consolidation pressure p0Formula (2)
As can be seen, equation 5 is for consolidation pressure before saturationThe reduction realizes the front consolidation pressure strength p0Reduction of (d). In formula 6, pcFor reference pressure, λ(s) and κ are respectively a plastic pressure index and an elastic pressure index corresponding to the slope of a specific volume (v) -effective stress natural logarithm (Inp) curve.
In a specific embodiment, the Baselina basic model (BBM model) of unsaturated soil considers the influence of suction force and the influence of shear strength and compression strength of soil body. A detailed discussion of this model includes
The Loading Collapse (LC) yield surface equation of the BBM model is expressed as
F in formula 7 is the loading yield function of collapsible, I1As a first invariant of net stress, J2Is a second invariant of bias stress, psWhich represents the tensile strength of the soil,is the slope of the main state line, expressed as
In formula 8Is the rubbing angle. Anterior consolidation pressure p in BBM model0Is shown as
In the formula 9, pcFor reference pressure, λ(s) and κ are respectively a plastic pressure index and an elastic pressure index corresponding to the slope of a specific volume (v) -effective stress natural logarithm (Inp) curve.
The independent variable s of the plastic pressure index lambda(s) is the suction force, lambda(s) being specified
λ(s) ═ λ (0) [ (1-r) exp (- β s) + r ] -formula 10
In equation 10, λ (0) is the plastic pressure index at saturation, and r and β are the rate parameter and the suction-stiffness control parameter of the λ(s) function.
Tensile Strength psIs written as
In formula 11, c represents cohesion. The cohesion force c is a function of the associated suction force and equivalent plastic strain and can be expressed by a linear formula, i.e.
In the formula 12 c0In order to initiate the cohesion force, the adhesive is,is the suction friction angle.
Suction Increase (SI) yield surface of BBM model, i.e.
F2＝s-s00-formula 13
In formula 13, F2Increasing yield function, s, for suction0Is unsaturated soil yield suction.
For unsaturated soil, the change of suction force causes volume deformation, and the recoverable elastic volume deformation caused by the change of suction force is expressed as
In equation 14 as is the increment of suction,for elastic volume strain increment, heIs elastic suction-bulk strain compliance, expressed as
Kappa in formula 15sIs a coefficient of elastic compliance, PatAt atmospheric pressure, e is the void ratio. The upper vector m is the unit hydrostatic pressure vector in the form of Voigt, which can be expressed for the Cosserat continuum
m＝[1 1 1 0 0 0 0]T-formula 16
Increasing the yield surface (F) in view of reaching the suction force2＝s-s0Not less than 0) and at the same time, when the suction force is increased (ds > 0), the soil will generate unrecoverable plastic volume deformation correspondingly, and the plastic volume strain can be expressed as
In the formula 17 areIs plastic volume strainIncrement, hpIs plastic suction-bulk strain compliance expressed as
In formula 18 ofsIs the coefficient of plastic compliance. Yield suction s0Can be expressed as
In formula 19Is the plastic volume strain caused by the suction effect.
The invention has the beneficial effects that: the method adopts a Baseline basic model which is more accordant with the properties of unsaturated soil for the constitutive model of the unsaturated soil, and considers the influence of suction and the influence of the shear strength and the compressive strength of the soil body in the constitutive model. The intensity reduction method for analyzing the stability of the unsaturated soil slope is based on a Cosserat-Biot continuum theory of solid-liquid-gas three-phase mechanics-seepage coupling, develops the coupling calculation of unsaturated soil mechanics and seepage, and considers the influence of the change of pore water and pore gas flow fields of the unsaturated soil slope under the action of rainfall and the change of soil body suction on the slope stability. The shear strength of the soil body is reduced by reducing the cohesive force and the friction angle of the soil body. In addition, the reduction of the compressive strength of the soil body is taken into account by reducing the front consolidation pressure of the soil body. The stability analysis of the unsaturated soil slope is carried out under a Cosserat continuum frame, the micro-rotation degree of freedom and the inner scale parameter are introduced, and the influence of the microscopic structure effect of the soil body on the stability of the macroscopic slope is considered to a certain extent. The method considers various influence factors and improves the accuracy of the stability analysis of the unsaturated soil slope.
Drawings
In order to more clearly explain the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and that for those skilled in the art, other related drawings can be obtained from these drawings without inventive effort.
Fig. 1 is a flowchart of a method for analyzing stability of an unsaturated soil slope according to an embodiment of the present application.
Fig. 2 is a flowchart of a method for analyzing the stability of an unsaturated soil slope according to an embodiment of the present application.
FIG. 3 is a slope pore water pressure profile under different rainfall conditions as provided in the examples of the present application.
Fig. 4 is a plastic strain distribution diagram of slope critical steady state under different rainfall conditions provided by the embodiment of the present application.
Detailed Description
To make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments obtained by a person of ordinary skill in the art without any inventive work based on the embodiments in the present application are within the scope of protection of the present application.
Thus, the following detailed description of the embodiments of the present application, as presented in the figures, is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments obtained by a person of ordinary skill in the art without any inventive work based on the embodiments in the present application are within the scope of protection of the present application.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
Examples
The mountain areas in China have extensive and large amounts of landslide disasters of unsaturated soil side slopes, and particularly the landslide disasters of the unsaturated soil side slopes are continuously generated along with the action of rainfall. In order to ensure the safety of engineering construction projects and the life and property safety of people, the research on the stability of unsaturated soil slopes is a considerable geological disaster research topic.
At present, the traditional method for researching the slope stability comprises the following steps: a limit balance method, a limit analysis method, a slip line field method, and the like. However, the methods do not consider the stress-strain relationship inside the soil body, are various stability analysis methods established on the basis of the extreme balance theory, cannot analyze the occurrence and development process of slope damage, simultaneously need to assume the shape and position of a slip fracture surface and the like to solve the safety coefficient, and are complex and not comprehensive in consideration.
The finite difference method of slope stability analysis that appeared later was the earliest slope stability analysis method implemented by computer numerical simulation. The finite difference method divides a solution domain into difference grids, and replaces continuous solution domains with finite grid nodes, although the defects of the previous methods are improved, the mechanical solution mode of the method has larger error and is still lack of accuracy, and the method is still to be improved.
The strength reduction finite element method developed on the basis inherits the advantages of finite element calculation, can reasonably and comprehensively consider the constitutive relation of the soil body, does not need to assume the shape of a sliding surface, and can obtain the sliding surface which is most easy to slide through calculation. The method can reflect the non-uniformity of the slope soil body and the non-linearity of deformation and sliding, can obtain a potential sliding surface and a corresponding safety coefficient through calculation, and can simulate mechanical responses such as slope internal stress strain and the like. Due to these advantages of finite element strength reduction, it has gained extensive research and application in recent years.
In recent years, the strength reduction finite element method is popularized to the analysis of the slope stability of unsaturated soil, and is widely concerned. The intensity reduction method applied to the unsaturated soil side slope emphasizes the influence of the change of the suction force in the unsaturated soil on the shear strength of the unsaturated soil, thereby having important influence on the stability of the unsaturated soil side slope. According to the intensity reduction method of the unsaturated soil slope, on the basis of the traditional intensity reduction method, a matrix suction item related to shear strength is reduced, and the contribution of the matrix suction to the slope stability is fully considered.
However, in the strength reduction method of the current slope stability analysis of unsaturated soil, the seepage of unsaturated soil is often simplified into a seepage model of saturated soil, and the coupling effect of the mechanical action of a solid skeleton and the seepage action of pore water and pore gas cannot be fully considered in the slope stability analysis. Moreover, the stability analysis of the unsaturated soil slope also often ignores the seepage effect of pore fluid of the slope, and does not consider the influence of the change of the suction field caused by the rainfall seepage effect on the slope stability in the used soil constitutive model.
In addition, when intensity reduction analysis is carried out, only the traditional soil mechanics constitutive model is adopted for reducing the shearing strength of the soil body of the side slope aiming at the unsaturated soil side slope, and the shearing strength and the compressive strength of the soil body are reduced simultaneously under the condition that the change of the soil body suction force is not fully considered. In addition, the intensity reduction method for analyzing the slope stability of the unsaturated soil is developed and applied on the basis of the traditional continuous medium mechanics, the consideration on the microscopic scale effect of the unsaturated soil is lacked, and the introduction of a regularization mechanism is lacked in the intensity reduction finite element simulation analysis of slope plastic slip.
Therefore, the inventor provides a stability analysis method for the hydraulic mechanical coupling of the unsaturated soil slope on the basis of a numerical simulation method and technology of the unsaturated soil of mechanical seepage coupling of a research team, adopts a Baseline Basic Model (BBM) which can accurately represent the hydraulic-mechanical properties of the unsaturated soil, and considers the influence of suction and the reduction of the shear strength and the compressive strength of a soil body in the stability analysis. The method analyzes the stability of the unsaturated soil slope under a Cosserat-Biot continuum framework, has the advantage of considering the influence of the microscopic structure effect of the soil body on the stability of the macroscopic slope to a certain extent, develops the coupling calculation of unsaturated soil mechanics and seepage, considers the seepage effect of pore water and pore gas of the unsaturated soil slope under the rainfall seepage effect, and provides a basis for accurately and reasonably researching the stability of the unsaturated soil slope in engineering practice.
Referring to fig. 1 and 2, the present application provides a method for analyzing the stability of hydraulic coupling of an unsaturated soil slope, including the following steps:
s100: and establishing a finite element numerical model of the side slope according to the geological model of the unsaturated soil side slope, physical and mechanical parameters of the soil body and hydraulic-mechanical load conditions.
S200: calculating and generating an initial stress field and a pore fluid pressure field of the side slope under the action of gravity and rainfall according to a Cosserat-Biot continuum finite element numerical simulation method of a Baseline basic model (BBM model) of unsaturated soil, and resetting an initial displacement field, a velocity field and a strain field of the side slope;
s300: setting reasonable upper limit value and lower limit value of the safety coefficient according to the initial requirement of the dichotomy of the slope safety coefficient solution;
s400: carrying out finite element calculation of intensity reduction method for slope stability analysis of unsaturated soil according to a Baseline basic model (BBM model) of unsaturated soil and a Cosserat-Biot continuum theory of solid, liquid and gas three-phase mechanics-seepage coupling;
s500: and (4) performing dichotomy cyclic calculation of the intensity reduction method of the unsaturated soil slope stability analysis to obtain an analysis result.
Wherein, the calculation step of obtaining the analysis result by the dichotomy cycle calculation of the intensity reduction method of the unsaturated soil slope stability analysis comprises
S510: and determining the current reduction coefficient as the average value of the upper limit value and the lower limit value of the safety factor.
S520: and respectively reducing the cohesive force, the friction angle and the front consolidation pressure of the soil body.
S530: and carrying out hydraulic-mechanical finite element calculation of the side slope under the action of gravity and rainfall load by using the reduced soil body parameters, and judging whether the calculation process is converged so as to judge the stability of the side slope.
Wherein if the calculation is convergent, the side slope is stable; otherwise, if the calculation is not convergent, the slope is unstable.
S540: if the side slope is stable, the lower limit value of the safety coefficient is expanded to be the current reduction coefficient, otherwise, if the side slope is unstable, the upper limit value of the safety coefficient is reduced to be the current reduction coefficient.
S550: and judging whether the difference between the upper and lower limit values of the safety coefficient meets the error requirement, if not, continuing the cyclic calculation of the dichotomy of the safety coefficient solution, and if so, skipping the iterative calculation.
S560: after the error requirement of the safety coefficient is met, setting the average value of the upper limit value and the lower limit value of the current safety coefficient as the final slope stability safety coefficient, reducing the strength parameter of the slope soil body under the safety coefficient, and calculating to obtain the analysis results of the stress, the strain, the displacement, the pore water pressure, the suction force and the like of the slope in the critical instability state.
In a specific embodiment, the intensity reduction method for analyzing the stability of the unsaturated soil slope implements the reduction of the shear strength of the soil body by reducing the cohesive force and the friction angle of the soil body, and in addition, the reduction of the compressive strength of the soil body is included by reducing the front consolidation pressure of the soil body. This process comprises
Based on the correlation theory of the strength reduction finite element method of slope stability analysis, the reduction cohesive force and the friction angle are considered, and the reduction formula is
In the formulas 1 and 2, F is a reduction coefficient, c,Respectively cohesive force and friction angle, c'),Are respectively asReduced cohesion and friction angle.
For the strength of unsaturated soil, the influence of suction is considered, and based on Fredlund strength reduction theory, the strength generated by the substrate suction s is required to be included in the total effective cohesive force, some
In the formula 3, c' is the cohesive force of the unsaturated soil after the reduction, and chi is a suction parameter.
Correspondingly, the effective shear strength of the unsaturated soil is reduced, and the reduced effective shear strength tau 'of the unsaturated soil is obtained'fCan be expressed as
As shown in formula 4, the relative cohesive force c and the friction angleThe reduction of the shear strength of the unsaturated soil is realized.
And (3) aiming at the BBM model of the unsaturated soil, reducing the front consolidation pressure strength of the unsaturated soil. To consolidation pressure before saturationPerforming reduction with the formula of
In formula 5The consolidation pressure before saturation after reduction.
According to the front consolidation pressure p0Formula (2)
As can be seen, equation 5 is for consolidation pressure before saturationThe reduction realizes the front consolidation pressure strength p0Reduction of (d). In formula 6, pcFor reference pressure, λ(s) and κ are respectively a plastic pressure index and an elastic pressure index corresponding to the slope of a specific volume (v) -effective stress natural logarithm (Inp) curve.
In a specific embodiment, the Baseline basic model (BBM model) of unsaturated soil considers the influence of suction force and the influence of the shear strength and the compression strength of the soil body. The basic Baselina model of unsaturated soil specifically comprises the following steps:
wherein, the Loading Collapse (LC) yield surface equation of the BBM model is expressed as
F in formula 7 is the loading yield function of collapsible, I1As a first invariant of net stress, J2Is a second invariant of bias stress, psWhich represents the tensile strength of the soil,is the slope of the main state line, expressed as
In formula 8Is a friction angle;
anterior consolidation pressure p in BBM model0Is shown as
In the formula 9, pcFor reference pressure, λ(s) and κ are defined by the specific volume (v) -effective stressThe plastic pressure index and the elastic pressure index corresponding to the slope of the logarithmic (Inp) curve;
the independent variable s of the plastic pressure index lambda(s) is the suction force, lambda(s) being specified
λ(s) ═ λ (0) [ (1-r) exp (- β s) + r ] -formula 10
In equation 10, λ (0) is the plastic pressure index at saturation, and r and β are the rate parameter and the suction-stiffness control parameter of the λ(s) function.
Tensile Strength psIs composed of
In formula 11, c is cohesive force, and the cohesive force c is a function of the associated suction force and the equivalent plastic strain and is expressed by a linear formula, namely
In the formula 12 c0In order to initiate the cohesion force, the adhesive is,is the suction friction angle;
suction Increase (SI) yield surface of BBM model, i.e.
F2＝s-s00-formula 13
In formula 13, F2Increasing yield function, s, for suction0Unsaturated soil yield suction;
for unsaturated soil, the change of suction force causes volume deformation, and the recoverable elastic volume deformation caused by the change of suction force is expressed as
In equation 14 as is the increment of suction,for elastic volume strain increment, heIs an elastic suctionForce-body strain compliance, expressed as
Kappa in formula 15sIs a coefficient of elastic compliance, PatAt atmospheric pressure, e is the void ratio. The upper vector m is the unit hydrostatic pressure vector in the form of Voigt, which can be expressed for the Cosserat continuum
m＝[1 1 1 0 0 0 0]T-formula 16
Increasing the yield surface (F) in view of reaching the suction force2＝s-s0Not less than 0) and at the same time, when the suction force is increased (ds > 0), the soil will generate unrecoverable plastic volume deformation, which is expressed as plastic volume strain
In the formula 17 areIncrease in plastic volume strain, hpIs plastic suction-bulk strain compliance expressed as
In formula 18 ofsIs the coefficient of plastic compliance. Yield suction s0Can be expressed as
In formula 19Is the plastic volume strain caused by the suction effect.
In order to verify the effectiveness and accuracy of the method for analyzing the stability of the hydraulic mechanical coupling of the unsaturated soil slope, the stability analysis of the unsaturated soil slope of the Minjiang upstream dry and warm valley under the rainfall action is considered.
Three different rainfall actions are set according to the local rainfall conditions in summer, and the rainfall actions are divided into three different intensities of 10mm/d of small rainfall, 50mm/d of medium rainfall and 100mm/d of heavy rainfall.
The strength reduction finite element method for slope stability analysis under the rainfall action is obtained: when the rainfall intensity is 10mm/d, the safety coefficient of the side slope is 1.56, and the side slope is stable; when the rainfall intensity is 50mm/d, the safety coefficient of the side slope is 1.23, and the side slope is basically stable; when the rainfall intensity is 100mm/d, the safety coefficient of the side slope is 0.95, and the side slope is unstable.
The pore water pressure and plastic strain distributions obtained by slope stability analysis under the rainfall intensity of a small amount of rainfall 10mm/d, a medium rainfall 50mm/d and a heavy rainfall 100mm/d are respectively shown in FIG. 3 and FIG. 4.
According to the slope stability analysis result, the slope safety coefficient is effectively obtained by the slope stability analysis strength reduction finite element method, the slope instability pore water seepage response and the specific slip failure mode are analyzed, and the slope stability is effectively analyzed.
The numerical simulation method of the unsaturated soil of mechanical seepage coupling provided by the invention adopts a Baseline basic model which better accords with the properties of the unsaturated soil, and the influence of suction and the influence of the shear strength and the compressive strength of the soil body are considered in the constitutive model. The intensity reduction method for analyzing the stability of the unsaturated soil slope reduces the shearing strength of the soil body by reducing the cohesive force and the friction angle of the soil body. In addition, the reduction of the compressive strength of the soil body is taken into account by reducing the front consolidation pressure of the soil body. The stability analysis of the unsaturated soil slope is carried out under a Cosserat continuum frame, the influence of the microcosmic structure effect of the soil body on the stability of a macroscopic slope is considered to a certain extent, and the stability of the unsaturated soil slope is reasonably and accurately analyzed.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims (4)
1. A method for analyzing stability of hydraulic mechanics coupling of unsaturated soil slope is characterized by comprising the following steps:
s100: establishing a finite element numerical model of the side slope according to the geological model of the unsaturated soil side slope, physical and mechanical parameters of the soil body and hydraulic mechanical load conditions;
s200: according to a Cosserat-Biot continuum finite element numerical simulation method of a Baselina basic model of unsaturated soil, calculating and generating an initial stress field and a pore fluid pressure field of a side slope under the action of gravity and rainfall, and resetting an initial displacement field, a velocity field and a strain field of the side slope;
s300: setting reasonable upper limit value and lower limit value of the safety coefficient according to the initial requirement of the dichotomy of the slope safety coefficient solution;
s400: carrying out finite element calculation of intensity reduction method for analyzing the slope stability of unsaturated soil according to a Baseline basic model of unsaturated soil and a Cosserat-Biot continuum theory of solid, liquid and gas three-phase mechanical seepage coupling;
s500: and (4) performing dichotomy cyclic calculation of the intensity reduction method of the unsaturated soil slope stability analysis to obtain an analysis result.
2. The method of claim 1, wherein the computing step of obtaining the analysis result by using a dichotomy cycle computation of an intensity reduction method of the unsaturated soil slope stability analysis comprises
S510: determining the current reduction coefficient as the average value of the upper limit value and the lower limit value of the safety coefficient;
s520: respectively reducing the cohesive force, the friction angle and the front consolidation pressure of the soil body;
s530: carrying out finite element calculation of hydrodynamics of the side slope under the action of gravity and rainfall load by using the reduced soil body parameters, and judging the stability of the side slope according to whether the calculation process is converged or not;
s540: if the side slope is stable, the lower limit value of the safety coefficient is expanded to be the current reduction coefficient, and if the side slope is unstable, the upper limit value of the safety coefficient is reduced to be the current reduction coefficient;
s550: judging whether the difference between the upper and lower limit values of the safety coefficient meets the error requirement, if not, continuing the cyclic calculation of the dichotomy of the safety coefficient solution, and if so, jumping out of the iterative calculation;
s560: after the error requirement of the safety coefficient is met, setting the average value of the upper limit value and the lower limit value of the current safety coefficient as the final slope stability safety coefficient, reducing the strength parameter of the slope soil body under the safety coefficient, and calculating to obtain the analysis results of stress, strain, displacement, pore water pressure and suction of the slope in the critical instability state.
3. The method for analyzing the stability of the hydraulic coupling of the unsaturated soil slope according to claim 1, wherein the intensity reduction method for analyzing the stability of the unsaturated soil slope specifically comprises the following steps:
based on the correlation theory of the strength reduction finite element method of slope stability analysis, the reduction cohesive force and the friction angle are considered, and the reduction formula is
In the formulas 1 and 2, F is a reduction coefficient, c,Respectively cohesive force and friction angle, c'),Respectively representing the cohesive force and the friction angle after the folding;
based on Fredlund's reduction of strength theory, the strength generated by the suction force s of the matrix is included in the total effective cohesion, some
In the formula 3, c' is the cohesive force of the unsaturated soil after the reduction, and chi is a suction parameter;
correspondingly, the effective shear strength of the unsaturated soil is reduced, and the reduced effective shear strength tau 'of the unsaturated soil is obtained'fIs shown as
Aiming at the BBM model of unsaturated soil, the front consolidation pressure intensity of the unsaturated soil is reduced, and the consolidation pressure before saturation is reducedPerforming reduction with the formula of
In the formula 5, the first step is,the consolidation pressure before saturation after reduction;
according to the front consolidation pressure p0Formula (2)
In formula 6, pcFor reference pressure, λ(s) and κ are respectively a plastic pressure index and an elastic pressure index corresponding to the slope of a specific volume (v) -effective stress natural logarithm (Inp) curve.
4. The method of claim 1, wherein the Baselina model of unsaturated soil considers the influence of suction and the shearing strength and compression strength of soil,
wherein, the Loading Collapse (LC) yield surface equation of the BBM model is expressed as
F in formula 7 is the loading yield function of collapsible, I1As a first invariant of net stress, J2Is a second invariant of bias stress, psWhich represents the tensile strength of the soil,is the slope of the main state line, expressed as
In formula 8Is a friction angle;
anterior consolidation pressure p in BBM model0Is shown as
In the formula 9, pcFor reference pressure, λ(s) and κ are respectively a plastic pressure index and an elastic pressure index corresponding to the slope of a specific volume (v) -effective stress natural logarithm (Inp) curve;
the independent variable s of the plastic pressure index lambda(s) is the suction force, lambda(s) being specified
λ(s) ═ λ (0) [ (1-r) exp (- β s) + r ] -formula 10
In the formula 10, λ (0) is a plastic pressure index in a saturated state, and r and β are a rate parameter and a suction-stiffness control parameter of a λ(s) function;
tensile Strength psIs composed of
In formula 11, c is cohesive force, and the cohesive force c is a function of the associated suction force and the equivalent plastic strain and is expressed by a linear formula, namely
In the formula 12 c0In order to initiate the cohesion force, the adhesive is,is the suction friction angle;
suction Increase (SI) yield surface of BBM model, i.e.
F2＝s-s00-formula 13
In formula 13, F2Increasing yield function, s, for suction0Unsaturated soil yield suction;
for unsaturated soil, the change of suction force causes volume deformation, and the recoverable elastic volume deformation caused by the change of suction force is expressed as
In equation 14 as is the increment of suction,for elastic volume strain increment, heIs elastic suction-bulk strain compliance, expressed as
Kappa in formula 15sIs a coefficient of elastic compliance, PatIs atmospheric pressure, e is the void ratio, and the upper vector m is the unit hydrostatic water in Voigt formThe pressure vector, for Cosserat continuum, can be expressed as
m＝[1 1 1 0 0 0 0]T-formula 16
Increasing the yield surface (F) in view of reaching the suction force2＝s-s0Not less than 0) and at the same time, when the suction force is increased (ds > 0), the soil will generate unrecoverable plastic volume deformation, which is expressed as plastic volume strain
In the formula 17 areIncrease in plastic volume strain, hpIs plastic suction-bulk strain compliance expressed as
In formula 18 ofsIs a coefficient of plastic compliance, yield suction s0Expressed as the law of hardening
In formula 19Is the plastic volume strain caused by the suction effect.
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