CN114722560A - Safety coefficient determination method based on soil slope strength reduction method - Google Patents

Safety coefficient determination method based on soil slope strength reduction method Download PDF

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CN114722560A
CN114722560A CN202111589824.3A CN202111589824A CN114722560A CN 114722560 A CN114722560 A CN 114722560A CN 202111589824 A CN202111589824 A CN 202111589824A CN 114722560 A CN114722560 A CN 114722560A
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slope
soil
maximum
strain
displacement
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CN114722560B (en
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龙云霄
曹新文
刘伟杰
殷柯
韦俊杰
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Chongqing Tiefa Jianxin Expressway Co ltd
Southwest Jiaotong University
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Southwest Jiaotong University
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Abstract

The invention discloses a safety coefficient determination method based on soil slope strength reduction, which comprises the following steps of: s1: collecting the strength parameters of the soil slope, and calculating the maximum slope displacement and the maximum slope strain of the soil slope; s2: and determining the safety coefficient of the soil slope according to the maximum slope displacement and the maximum slope strain of the slope. The method overcomes the defects of inaccurate calculation and large error of the conventional intensity reduction method, takes the maximum shear strain of 15-20% as an index for judging the instability of the soil slope, and can prevent and forecast the instability damage of the slope by monitoring the instability index of the soil body of the slope.

Description

Safety coefficient determination method based on soil slope strength reduction method
Technical Field
The invention belongs to the technical field of slope engineering, and particularly relates to a safety coefficient determination method based on a soil slope strength reduction method.
Background
In classical soil mechanics, the safety coefficient of a soil slope is calculated by using a strip division method. The strip division method can be divided into a Fellenius method, a BIShop method, a Janbu method, a Morgenstrin-Price method and the like according to assumed conditions among strips, and the safety factors of the side slope are directly calculated by the methods. However, in the numerical analysis method, the stress, strain and displacement of the slope unit calculated by the numerical method cannot obtain the safety coefficient of the slope, so that the stable state of the slope cannot be judged. For this reason, it is proposed to use intensity subtraction for the calculation of the safety factor.
Because the software and the calculation method are different, when the finite element or discrete element numerical calculation software adopts the strength reduction method to analyze the slope stability, the method for acquiring the slope stability safety coefficient is different, and the following 3 judgment methods are generally adopted. (1) Numerical calculations do not converge: when the finite element software applies the strength reduction method, the material parameters set the change step length through a program, and the automatic reduction of the strength parameters is realized. And if the calculated force imbalance coefficient still cannot meet the default value of the software after the strength parameter of a certain level reaches the iteration number set by the software, the slope is considered to be unstable, and the software calculation is not converged. The reduction factor corresponding to the intensity parameter of the previous stage of this stage of intensity parameters is considered as a safety factor. (2) Displacement mutation: under the condition that the intensity parameters are continuously decreased, when the calculated displacement value of the model under a certain intensity parameter is greatly changed compared with the displacement value calculated under the previous intensity parameter, the slope is indicated to have unlimited relative displacement, displacement mutation and slope instability. And at the moment, the intensity fold deceleration parameter corresponding to the mutation point can be used as the anti-skid stability safety factor of the slope. (3) The plastic yield area is communicated: when the soil body gradually generates plastic strain, the soil body is shown to generate unrecoverable residual deformation, the stress state of the soil body exceeds the strength yield criterion, the soil body is damaged, the plastic zone is gradually communicated along with the continuous reduction of the strength parameter, and the slope is instable at the moment.
In software adopting the first judgment method, the numerical calculation is not converged by generally designating a certain number of iterations, and when the calculated number of iterations exceeds the designated number of iterations, the force imbalance coefficient still cannot meet the program default value, and the slope is considered to be unstable. Therefore, the safety factor depends on the specified iteration times to some extent, and the damage condition of the slope cannot be completely reflected. In addition, the force imbalance coefficient is an artificial parameter for measuring the convergence degree in the calculation process, can be assumed artificially, is not a specific index of a numerical model, and has high randomness. For example, the force imbalance coefficient can be determined to be 1e-5 or 1e-7 in some model calculations, and the smaller the force imbalance coefficient is, the more accurate the iterative convergence is. In software adopting the second judgment method, when the displacement is mutated, the displacement obtained by calculation often exceeds the size of the displacement in the actual engineering, so that people feel unrealistic. In software adopting the third judgment method, when the plastic yield area is communicated, the displacement is already large, and the local displacement exceeds the displacement which cannot be generated by the actual engineering.
Disclosure of Invention
The invention aims to solve the problems and provides a safety coefficient determination method based on soil slope strength reduction.
The technical scheme of the invention is as follows: a safety coefficient determination method based on soil slope strength reduction comprises the following steps:
s1: collecting the strength parameters of the soil slope, and calculating the maximum slope displacement and the maximum slope strain of the soil slope;
s2: and determining the safety coefficient of the soil slope according to the maximum slope displacement and the maximum slope strain of the slope.
Further, in step S1, the specific method for calculating the maximum slope displacement and the maximum slope strain of the soil slope is as follows: reducing the collected intensity parameters of the soil slope according to a set proportion, calculating the corresponding slope displacement and slope strain according to the reduced intensity parameters, and determining the maximum slope displacement SmaxAnd maximum slope strain epsilonmax。
Further, in step S1, the maximum slopeDisplacement SmaxThe relation of (A) is as follows:
Figure BDA0003428720950000031
wherein F (-) represents a slope displacement function, FsThe safety factor is shown, c represents the cohesive force of the soil body,
Figure BDA0003428720950000032
representing the internal friction angle of the soil body, and E representing the modulus of the soil;
maximum slope strain epsilonmaxThe relation of (A) is as follows:
Figure BDA0003428720950000033
wherein f' (. cndot.) represents a slope strain function.
Further, in step S2, the specific method for determining the safety factor is as follows: based on the maximum slope displacement and the maximum slope strain, the reduction coefficient is taken as a horizontal axis, the slope displacement or the slope strain is taken as a vertical axis, a curve is drawn, and in the curve, the strength parameter after reduction is positioned at the maximum slope strain epsilonmaxDetermining 15% of the side slope as a failure state, and determining the safety factor of the side slope according to the previous-stage strength parameter.
Further, in step S2, the cohesive force c corresponding to the n-level strength parameter when the slope is brokennAnd angle of internal friction
Figure BDA0003428720950000034
The calculation formulas of (A) and (B) are respectively as follows:
cn＝c(1-f)
Figure BDA0003428720950000035
wherein f represents a reduction coefficient, c represents cohesive force of a soil body,
Figure BDA0003428720950000036
indicating the internal friction angle of the soil mass.
The invention has the beneficial effects that: the method overcomes the defects of inaccurate calculation and large error of the conventional intensity reduction method, takes the maximum shear strain of 15-20% as an index for judging the instability of the soil slope, and can prevent and forecast the instability damage of the slope by monitoring the instability index of the soil body of the slope. The breaking point is generally 15% of the maximum shear strain.
Drawings
FIG. 1 is a flow chart of a safety coefficient determination method based on soil slope strength reduction;
FIG. 2 is a schematic diagram of displacement and shear strain under various operating conditions.
Detailed Description
The embodiments of the present invention will be further described with reference to the accompanying drawings.
As shown in fig. 1, the invention provides a method for determining a safety factor based on a soil slope strength reduction method, which comprises the following steps:
s1: collecting the strength parameters of the soil slope, and calculating the maximum slope displacement and the maximum slope strain of the soil slope;
s2: and determining the safety coefficient of the soil slope according to the maximum slope displacement and the maximum slope strain of the slope.
In the embodiment of the present invention, in step S1, the specific method for calculating the maximum slope displacement and the maximum slope strain of the soil slope is as follows: reducing the collected intensity parameters of the soil slope according to a set proportion, calculating the corresponding slope displacement and slope strain according to the reduced intensity parameters, and determining the maximum slope displacement SmaxAnd maximum slope strain epsilonmax。
In the embodiment of the invention, in the step S1, the maximum slope displacement SmaxThe relation of (A) is as follows:
Figure BDA0003428720950000041
wherein f (-) represents a slope displacement function，FsThe safety factor is shown, c represents the cohesive force of the soil body,
Figure BDA0003428720950000042
representing the internal friction angle of the soil body, and E representing the modulus of the soil;
maximum slope strain epsilonmaxThe relation of (A) is as follows:
Figure BDA0003428720950000043
wherein f' (. cndot.) represents a slope strain function.
In the embodiment of the present invention, in step S2, the specific method for determining the safety factor is as follows: based on the maximum slope displacement and the maximum slope strain, the reduction coefficient is taken as a horizontal axis, the slope displacement or the slope strain is taken as a vertical axis, a curve is drawn, and in the curve, the strength parameter after reduction is positioned at the maximum slope strain epsilonmaxDetermining 15% of the side slope as a failure state, and determining the safety factor of the side slope according to the previous-stage strength parameter. It is generally considered that the state of failure is reached when the maximum strain is equal to or greater than 15%. The corresponding order is taken as the intensity.
In the embodiment of the invention, in step S2, the cohesive force c corresponding to n-level strength parameters is adopted when the side slope is damagednAnd angle of internal friction
Figure BDA0003428720950000044
The calculation formulas of (A) and (B) are respectively as follows:
cn＝c(1-f)
Figure BDA0003428720950000051
wherein f represents a reduction coefficient, c represents cohesive force of a soil body,
Figure BDA0003428720950000052
indicating the internal friction angle of the soil mass.
The technical solution of the present invention will be described below with reference to specific examples.
When the reduction coefficient is specifically calculated, for convenience of explanation, the calculation of each reduction stage is referred to as a working condition, that is, the initial calculation is a working condition one, and so on. According to the reduction calculation method provided by the invention, the initial strength parameter is taken as the working condition 1, the strength parameter is reduced according to a reduction coefficient method, calculation is carried out under different working conditions, the calculation of the slope angle 45-degree slope three-dimensional model is not converged under the working condition 6, the calculation result values of the displacement and the strain of the working condition 1 to the working condition 5 are shown in a table 1, and the variation trend of the maximum value of the displacement and the maximum value of the shear strain along with the increasing reduction coefficient is shown in a figure 2.
TABLE 1
Figure BDA0003428720950000053
It can be seen that the maximum displacement value of the working condition 4 (point B in fig. 2) is increased by 0.08m compared with the working condition 3 (point a in fig. 2), the maximum shear strain value is increased by 7.0%, the maximum displacement value of the working condition 5 (point C in fig. 2) is increased by 0.18m compared with the working condition 4, the maximum shear strain value is increased by 41.6%, the displacement and strain value of the working condition 5 (point C in fig. 2) are mutated, and the shear strain of the working condition 5 (point C in fig. 2) has reached 54.30%, which indicates that the soil body has already entered a plastic state, is damaged, and the slope loses stability at this time. Thus, condition 4 (point B in FIG. 2) is determined to be the critical failure point, corresponding to FsThe safety factor is set.
The working principle and the process of the invention are as follows: in the shear strain test, it is generally considered that shear failure occurs when the shear strain is greater than 15%, and similarly, on an actual side slope, when the maximum shear strain at a certain position is greater than 15%, the position has already reached a limit equilibrium state, which indicates that the side slope has already reached a slow limit equilibrium state, and the side slope is unstable. However, since the maximum shear strain calculated in the calculation is not just 15% but a value larger than 15%, a range of 15 to 20% of the maximum shear strain is selected as a method for determining the slope instability.
The invention has the beneficial effects that: the method overcomes the defects of inaccurate calculation and large error of the conventional intensity reduction method, takes the maximum shear strain of 15-20% as an index for judging the instability of the soil slope, and can prevent and forecast the instability damage of the slope by monitoring the instability index of the soil body of the slope.
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.

Claims (5)

1. A safety coefficient determination method based on soil slope strength reduction is characterized by comprising the following steps:
s1: collecting the strength parameters of the soil slope, and calculating the maximum slope displacement and the maximum slope strain of the soil slope;
s2: and determining the safety coefficient of the soil slope according to the maximum slope displacement and the maximum slope strain of the slope.
2. The method for determining the safety factor based on the soil slope strength reduction method according to claim 1, wherein in the step S1, the specific method for calculating the maximum slope displacement and the maximum slope strain of the soil slope is as follows: reducing the collected intensity parameters of the soil slope according to a set proportion, calculating the corresponding slope displacement and slope strain according to the reduced intensity parameters, and determining the maximum slope displacement SmaxAnd maximum slope strain epsilonmax。
3. The method for determining the safety factor based on the soil slope strength reduction method according to claim 2, wherein in the step S1, the maximum slope displacement S ismaxThe relation of (A) is as follows:
Figure FDA0003428720940000011
wherein F (-) represents a slope displacement function, FsThe safety factor is shown, c represents the cohesive force of the soil body,
Figure FDA0003428720940000012
representing the internal friction angle of the soil body, and E representing the modulus of the soil;
maximum slope strain epsilonmaxThe relation of (A) is as follows:
Figure FDA0003428720940000013
wherein f' (. cndot.) represents a slope strain function.
4. The method for determining the safety factor based on the soil slope strength reduction method according to claim 1, wherein in the step S2, the specific method for determining the safety factor is as follows: based on the maximum slope displacement and the maximum slope strain, the reduction coefficient is taken as a horizontal axis, the slope displacement or the slope strain is taken as a vertical axis, a curve is drawn, and in the curve, the strength parameter after reduction is positioned at the maximum slope strain epsilonmaxDetermining the 15% of the side slope as a destruction state, and determining the safety factor of the side slope according to the previous-stage strength parameter. It is generally considered that the state of failure is reached when the maximum strain is equal to or greater than 15%. The corresponding order is taken as the intensity.
5. The method for determining the safety factor based on the soil slope strength reduction method according to claim 4, wherein in the step S2, the cohesive force c corresponding to n-level strength parameters is obtained when the slope is damagednAnd angle of internal friction
Figure FDA0003428720940000021
The calculation formulas of (A) and (B) are respectively as follows:
cn＝c(1-f)
Figure FDA0003428720940000022
wherein f represents a reduction coefficient, c represents cohesive force of soil,
Figure FDA0003428720940000023
indicating the internal friction angle of the soil mass.
CN202111589824.3A 2021-12-23 2021-12-23 Safety coefficient determination method based on soil slope strength folding and subtracting method Active CN114722560B (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106874649A (en) * 2017-01-09 2017-06-20 东北电力大学 A kind of homogeneous slope stability_intensity reduction method INSTABILITY CRITERION
CN107330182A (en) * 2017-06-28 2017-11-07 西北农林科技大学 The method that strength degradation based on humidification conditions calculates safety factor of slope
CN111291996A (en) * 2020-02-17 2020-06-16 绍兴文理学院 Three-parameter strength reduction method for slope stability evaluation
CN111324942A (en) * 2019-12-27 2020-06-23 昆明理工大学 Seismic slope stability analysis method considering progressive damage of sliding surface power
CN112307549A (en) * 2020-11-02 2021-02-02 中南大学 Slope safety coefficient calculation method and instability judgment method for locking section structure
CN113742827A (en) * 2021-09-03 2021-12-03 招商局重庆交通科研设计院有限公司 Method for constructing highway slope monitoring network system based on finite difference analysis

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Publication number Priority date Publication date Assignee Title
CN106874649A (en) * 2017-01-09 2017-06-20 东北电力大学 A kind of homogeneous slope stability_intensity reduction method INSTABILITY CRITERION
CN107330182A (en) * 2017-06-28 2017-11-07 西北农林科技大学 The method that strength degradation based on humidification conditions calculates safety factor of slope
CN111324942A (en) * 2019-12-27 2020-06-23 昆明理工大学 Seismic slope stability analysis method considering progressive damage of sliding surface power
CN111291996A (en) * 2020-02-17 2020-06-16 绍兴文理学院 Three-parameter strength reduction method for slope stability evaluation
CN112307549A (en) * 2020-11-02 2021-02-02 中南大学 Slope safety coefficient calculation method and instability judgment method for locking section structure
CN113742827A (en) * 2021-09-03 2021-12-03 招商局重庆交通科研设计院有限公司 Method for constructing highway slope monitoring network system based on finite difference analysis

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