Stability evaluation method for shallow vegetation slope

Abstract

The invention discloses a stability evaluation method for a shallow vegetation slope, belongs to the technical field of slope engineering, and aims to solve the technical problem of large slope stability evaluation error caused by the fact that a model is insufficient and does not consider a transpiration attenuation function of vegetation in the prior art. Comprising the following steps: S10, sampling and measuring parameters; s20, constructing an unsaturated vegetation slope model; s30, performing model calculation; s40, carrying out iterative decoupling; s50, solving a safety coefficient; and S60, determining the stability state of each potential slip plane of the slope, and comparing the safety coefficients of different potential slip planes with a safety coefficient threshold to obtain a stability evaluation result. According to the stability evaluation method for the shallow vegetation slope, the stability evaluation accuracy can be better and effectively improved, and effective help is provided for slope instability and landslide disaster early warning.

Description

Technical Field

[0001] The invention relates to the technical field of slope engineering, and in particular to a stability evaluation method for shallow vegetation slopes. Background Art

[0002] When natural slopes encounter rainfall, the water content of the soil will rise rapidly, causing the matrix suction in the slope soil to decrease, thereby weakening the shear strength of the soil and greatly reducing the stability of the slope. This slope instability caused by rainfall may lead to natural disasters such as landslides and mudslides, seriously threatening the lives and safety of residents in the area and causing huge economic losses. However, natural slopes are usually covered by vegetation. Vegetation is not only an important part of the slope ecosystem, but also has a direct impact on the moisture status and matrix suction of the slope soil through root water absorption and leaf transpiration. During the process of rainfall infiltration, vegetation absorbs moisture from the soil to the surface through its roots and releases it into the atmosphere through transpiration, thereby reducing the moisture content in the soil and increasing the matrix suction. This transpiration effectively improves the shear strength of the soil, and thus can improve the stability of the slope to a certain extent.

[0003] In existing studies, shallow vegetation slope models are generally based on the Richards equation to describe the flow of water in unsaturated soil. These models usually only consider the effect of water absorption by vegetation roots on slope water migration, and simplify the transpiration of vegetation into the source term in the Richards equation. However, these models do not fully consider the transpiration attenuation function of vegetation, that is, the regulation of plant water absorption capacity with changes in matrix suction. The transpiration attenuation function affects the transpiration of vegetation, thereby affecting the final calculated slope stability. Therefore, ignoring this factor may cause the model to produce large errors when predicting slope safety under rainfall conditions. Summary of the invention

[0004] The purpose of the present invention is to provide a stability evaluation method for shallow vegetation slopes to solve the technical problem that the model in the prior art does not fully consider the transpiration attenuation function of vegetation, thereby resulting in large errors in slope stability evaluation.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for evaluating the stability of a shallow vegetation slope, comprising the following steps:

[0007] S10, sampling and parameter determination, sampling the target slope to obtain soil characteristic parameters and vegetation characteristic parameters;

[0008] S20, constructing an unsaturated vegetation slope model, and constructing an unsaturated vegetation slope model including a matrix suction regulation mechanism with water content change and a transpiration attenuation function based on soil characteristic parameters and vegetation characteristic parameters;

[0009] S30, model calculation, inputting the measured parameters into the unsaturated vegetation slope model to obtain the relative permeability under steady state;

[0010] S40, iterative decoupling, decoupling the evaporation attenuation function from the relative permeability in the steady state through numerical iteration method, and obtaining the pore water content at different depths of the slope;

[0011] S50, solving the safety factor, and calculating the safety factor of different potential slip surfaces by limit equilibrium analysis method;

[0012] S60, determining the stability state of each potential slip surface of the slope, comparing and determining the safety factors of different potential slip surfaces with the safety factor threshold, and obtaining a stability evaluation result.

[0013] Optionally or preferably, the soil characteristic parameters in step S10 include a soil matrix suction and water relationship curve, soil hydraulic parameters, soil volume moisture content, soil residual volume moisture content, and soil saturated volume moisture content;

[0014] The vegetation characteristic parameters include the geometric distribution function of plant roots with depth and the plant transpiration attenuation function.

[0015] Optionally or preferably, step S30 includes the following steps:

[0016] S31. Define dimensionless parameter z * , L * , k * ,

[0017] z * = zcosβ

[0018] L * =Lcosβ

[0019]

[0020]

[0021] k*=k / k s

[0022]

[0023] Among them, z is the vertical coordinate, x is the horizontal coordinate, L is the total layer thickness, L1 is the thickness of the rootless layer, L2 is the thickness of the rooted layer, k is the permeability coefficient of the soil, q0 is the rainfall intensity in steady state, k s is the hydraulic parameter of the soil;

[0024] S32. Calculate the relative permeability of the slope in steady state

[0025]

[0026] Among them, α is the hydraulic parameter of the soil, ψ0 is the water potential, and β is the slope inclination;

[0027]

[0028] is the transpiration decay function,

[0029]

[0030] k1=1 / [log(h2)-log(h1)]

[0031] b1=-k1log(h1)

[0032] k2=1 / [log(h3)-log(h4)]

[0033] b2=-k2log(h4)

[0034] in, is the matrix suction, h1, h2, h3, h4 are the attenuation characteristic parameters of plants;

[0035] g(z') is the geometric distribution parameter of plant roots,

[0036]

[0037] H(·) is a unit step function, which is used to distinguish and represent rooted and non-rooted regions:

[0038]

[0039] Optionally or preferably, the iterative decoupling method in step S40 is:

[0040] S41, Select The initial value is

[0041] S42. Calculate transpiration attenuation function

[0042] S43. Calculate relative permeability

[0043] S44, get new parameter value

[0044] S45, if Based on the new parameter value Calculate the final relative permeability and output the pore water pressure distribution u w ; Otherwise, repeat S42 to S45.

[0045] Optionally or preferably, the pore water pressure distribution u in S45 w The calculation method is:

[0046]

[0047] Optionally or preferably, the method for solving the safety factor in S50 is:

[0048]

[0049]

[0050] Among them, F s is the safety factor, c' is the effective cohesion of the soil or root-soil composite at a specific depth, φ' is the effective friction angle of the soil or root-soil composite, β is the angle between the sliding surface and the horizontal line, γ d is the dry weight of soil or root-soil complex, γ d is the water density, Z is the vertical distance from the sliding surface to the slope surface, H is the vertical height of the slope surface, χ is the effective saturation, θ is the volumetric water content of the soil, and θ r is the residual volume moisture content, θ s is the saturated volumetric water content.

[0051] Optionally or preferably, the method for determining the stability state of each potential slip surface of the slope in S60 is:

[0052] If the safety factor is lower than the instability threshold, the slip surface is at risk of instability;

[0053] Otherwise, there is no risk of instability.

[0054] Based on the above technical solution, the present invention can at least produce the following technical effects:

[0055] The present invention provides a stability evaluation method for shallow vegetation slopes, which can accurately simulate the role of vegetation in slope moisture migration and matrix suction changes taking into account the effect of transpiration attenuation function. Through this model, the moisture distribution, matrix suction and safety factor of the slope in a steady state under rainfall conditions can be calculated, thereby improving the performance of the model in terms of calculation accuracy and providing a more reliable basis for slope safety evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a flow chart of the stability evaluation method for shallow vegetation slope of the present invention;

[0057] Figure 2 It is a schematic diagram of the slope structure in the stability evaluation method for shallow vegetation slope of the present invention;

[0058] Figure 3 It is a flow chart of the iterative decoupling process in the stability evaluation method for shallow vegetation slopes of the present invention. DETAILED DESCRIPTION

[0059] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work belong to the scope of protection of the present invention.

[0060] Example

[0061] See also Figures 1 to 3 , a stability evaluation method for shallow vegetation slopes, comprising the following steps:

[0062] S10, sampling and parameter determination, sampling the target slope to obtain soil characteristic parameters and vegetation characteristic parameters;

[0063] In this embodiment, the soil characteristic parameters include the soil matrix suction and water relationship curve (soil-water characteristic curve), soil hydraulic parameters, soil volume moisture content, soil residual volume moisture content, soil saturated volume moisture content, soil effective cohesion and soil effective friction angle;

[0064] Vegetation characteristic parameters include the geometric distribution function of plant roots with depth and the plant transpiration attenuation function.

[0065] S20, constructing an unsaturated vegetation slope model, and constructing an unsaturated vegetation slope model including a matrix suction regulation mechanism with water content change and a transpiration attenuation function based on soil characteristic parameters and vegetation characteristic parameters;

[0066] Based on the above soil characteristic parameters and plant characteristic parameters, a mathematical model of the component unsaturated plant slope is proposed. The model integrates the regulation mechanism of matrix suction with water content change, and reflects the dynamic absorption process of soil moisture by vegetation based on the soil-water characteristic curve and transpiration attenuation function.

[0067] S30, model calculation, inputting the measured parameters into the unsaturated vegetation slope model to obtain the relative permeability under steady state;

[0068] S31. Define dimensionless parameter z * , L * , k * ,

[0069] z * = zcosβ

[0070] L * =Lcosβ

[0071]

[0072]

[0073] k*=k / k s

[0074]

[0075] Among them, z is the vertical coordinate, x is the horizontal coordinate, L is the total layer thickness, L1 is the thickness of the rootless layer, L2 is the thickness of the rooted layer, k is the permeability coefficient of the soil, q0 is the rainfall intensity in steady state, k s is the hydraulic parameter of the soil;

[0076] S32. Calculate the relative permeability of the slope in steady state

[0077]

[0078] Among them, α is the hydraulic parameter of the soil, ψ0 is the water potential, and β is the slope inclination;

[0079]

[0080] is the transpiration decay function,

[0081]

[0082] k1=1 / [log(h2)-log(h1)]

[0083] b1=-k1log(h1)

[0084] k2=1 / [log(h3)-log(h4)]

[0085] b2=-k2log(h4)

[0086] in, is the matrix suction, h1, h2, h3, and h4 are the attenuation characteristic parameters of the plant, which can be measured using a moisture content sensor and a matrix suction sensor;

[0087] g(z') is the geometric distribution parameter of plant roots, which can be determined according to different plant types. Its expression is as follows:

[0088]

[0089] H(·) is a unit step function, which is used to distinguish and represent rooted and non-rooted regions:

[0090]

[0091] S40, iterative decoupling, decoupling the evaporation attenuation function from the relative permeability in the steady state through numerical iteration method, and obtaining the pore water content at different depths of the slope;

[0092] It should be noted that and are coupled, in order to obtain and It needs to be iteratively decoupled, including the following steps:

[0093] S41, Select The initial value is

[0094] S42. Calculate transpiration attenuation function

[0095] S43. Calculate relative permeability

[0096] S44, get new parameter value

[0097] S45, if Based on the new parameter value Calculate the final relative permeability and output the pore water pressure distribution u w ; Otherwise, repeat S42 to S45.

[0098] In this embodiment, the calculation method of the pore water pressure is:

[0099]

[0100] S50, solving the safety factor, and calculating the safety factor of different potential slip surfaces by limit equilibrium analysis method;

[0101] In this embodiment, the method for calculating the safety factor is:

[0102]

[0103]

[0104] Among them, F s is the safety factor, c' is the effective cohesion of the soil or root-soil composite at a specific depth, φ' is the effective friction angle of the soil or root-soil composite, β is the angle between the sliding surface and the horizontal line, γ d is the dry weight of soil or root-soil complex, γ d is the water density, Z is the vertical distance from the sliding surface to the slope surface, H is the vertical height of the slope surface, χ is the effective saturation, θ is the volumetric water content of the soil, and θ r is the residual volume moisture content, θ s is the saturated volumetric water content.

[0105] S60, determining the stability state of each potential slip surface of the slope, comparing and determining the safety factors of different potential slip surfaces with the safety factor threshold, and obtaining a stability evaluation result.

[0106] In this embodiment, the method for determining the stability state of each potential slip surface of the slope is: if the safety factor is lower than the instability threshold, the slip surface has an instability risk; otherwise, it does not have an instability risk.

[0107] Specifically, the calculation results will generate a safety factor distribution diagram for each potential sliding surface. Based on the preset safety factor threshold (for example, 1.0 is the instability threshold), the stability state of each sliding surface of the slope can be determined; if the safety factor calculated by the model is lower than the threshold, it indicates that the sliding surface has an instability risk; otherwise, it does not have an instability risk; the dynamic simulation of the model can also show the changing trend of the safety factor of different sliding surfaces and predict potential unstable areas.

[0108] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "mounted / connected", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0109] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A stability evaluation method for shallow vegetation slopes, characterized in that: The following steps are involved: S10, sampling and parameter determination, sampling the target slope to obtain soil characteristic parameters and vegetation characteristic parameters; S20, constructing an unsaturated vegetation slope model, and constructing an unsaturated vegetation slope model including a matrix suction regulation mechanism with water content change and a transpiration attenuation function based on soil characteristic parameters and vegetation characteristic parameters; S30, model calculation, inputting the measured parameters into the unsaturated vegetation slope model to obtain the relative permeability under steady state; S40, iterative decoupling, decoupling the evaporation attenuation function from the relative permeability in the steady state through numerical iteration method, and obtaining the pore water content at different depths of the slope; S50, solving the safety factor, and calculating the safety factor of different potential slip surfaces by limit equilibrium analysis method; S60, determining the stability state of each potential slip surface of the slope, comparing and determining the safety factors of different potential slip surfaces with the safety factor threshold, and obtaining a stability evaluation result.

2. The stability evaluation method for shallow vegetation slope according to claim 1 is characterized in that: The soil characteristic parameters in step S10 include a soil matrix suction and water relationship curve, soil hydraulic parameters, soil volume moisture content, soil residual volume moisture content, soil saturated volume moisture content, soil effective cohesion, and soil effective friction angle; The vegetation characteristic parameters include the geometric distribution function of plant roots with depth and the plant transpiration attenuation function.

3. The stability evaluation method for shallow vegetation slope according to claim 1 is characterized in that: Step S30 includes the following steps: S31. Define dimensionless parameter z * , L * , k * , With * =zcosβ k*=k / k s Among them, z is the vertical coordinate, x is the horizontal coordinate, L is the total layer thickness, L1 is the thickness of the rootless layer, L2 is the thickness of the rooted layer, k is the permeability coefficient of the soil, q0 is the rainfall intensity in steady state, k s is the hydraulic parameter of the soil; S32. Calculate the relative permeability of the slope in steady state Among them, α is the hydraulic parameter of the soil, ψ0 is the water potential, and β is the slope inclination; is the transpiration decay function, k1=1 / [log(h2)-log(h1)] b1=-k1log(h1) k2=1 / [log(h3)-log(h4)] b2=-k2log(h4) in, is the matrix suction, h1, h2, h3, h4 are the attenuation characteristic parameters of plants; g(z') is the geometric distribution parameter of plant roots, H(·) is a unit step function, which is used to distinguish and represent rooted and non-rooted regions:

4. The stability evaluation method for shallow vegetation slope according to claim 3 is characterized in that: The iterative decoupling method in step S40 is: S41, Select The initial value is S42. Calculate transpiration attenuation function S43. Calculate relative permeability S44, get new parameter value S45, if Based on the new parameter value Calculate the final relative permeability and output the pore water pressure distribution u w ; Otherwise, repeat S42 to S45.

5. The stability evaluation method for shallow vegetation slope according to claim 4 is characterized in that: Pore ​​water pressure distribution in S45 w The calculation method is:

6. The stability evaluation method for shallow vegetation slope according to claim 1, characterized in that: The method for solving the safety factor in S50 is: Among them, F s is the safety factor, c' is the effective cohesion of the soil or root-soil composite at a specific depth, φ' is the effective friction angle of the soil or root-soil composite, β is the angle between the sliding surface and the horizontal line, γ d is the dry weight of soil or root-soil complex, γ d is the water density, Z is the vertical distance from the sliding surface to the slope surface, H is the vertical height of the slope surface, χ is the effective saturation, θ is the volumetric water content of the soil, and θ r is the residual volume moisture content, θ s is the saturated volumetric water content.

7. The method for evaluating the stability of a shallow vegetation slope according to claim 1, characterized in that: The method for determining the stability state of each potential slip surface of the slope in S60 is: If the safety factor is lower than the instability threshold, the slip surface is at risk of instability; Otherwise, there is no risk of instability.

Images