CN114722560B - Safety coefficient determination method based on soil slope strength folding and subtracting method - Google Patents
Safety coefficient determination method based on soil slope strength folding and subtracting method Download PDFInfo
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Abstract
The invention discloses a safety coefficient determination method based on soil slope strength folding and subtracting method, which comprises the following steps: s1: collecting the intensity parameters of the soil slope, and calculating the maximum slope displacement and the maximum slope strain; 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 invention overcomes the defects of inaccurate calculation and larger error of the traditional strength folding and subtracting method, takes the maximum shearing strain reaching 15-20% as the instability index for judging 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
Technical Field
The invention belongs to the technical field of slope engineering, and particularly relates to a safety coefficient determination method based on soil slope strength folding and subtracting method.
Background
In classical soil mechanics, a stripe method is used to calculate the safety coefficient of the soil slope. The stripe dividing method can be further classified into a Fellenius method, a BIshop method, a Janbu method, a Morgenstern-Price method and the like according to the assumption conditions among stripes, and the safety coefficient of the side slope is 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, and thus the stable state of the slope cannot be determined. For this purpose, it is proposed to use intensity folding and subtraction to calculate the safety factor.
Because of different software and calculation methods, when the finite element or discrete element numerical calculation software adopts intensity folding and subtracting method to perform slope stability analysis, the method for obtaining the slope number stability safety coefficient is different, and the following 3 judgment methods are generally available. (1) numerical computation does not converge: when the finite element software applies the intensity folding and subtracting method, the material parameters are set to change step length through a program, so that the automatic folding and subtracting of the intensity parameters is realized. If the calculated force unbalance coefficient still cannot meet the default value of the software after the intensity parameter of a certain stage reaches the iteration number set by the software, the slope is considered to be unstable, and the software calculation is not converged. The reduction coefficient corresponding to the intensity parameter of the preceding stage of the intensity parameter of this stage is regarded as the safety coefficient. (2) a shift 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 changed greatly compared with the calculated displacement value under the previous intensity parameter, the situation shows that the slope has unlimited relative displacement, sudden displacement change and instability occurs. At the moment, the intensity reduction speed parameter corresponding to the mutation point can be used as an anti-slip stable safety coefficient of the side slope. (3) plastic yield zone penetration: 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 area is gradually communicated along with the continuous reduction of the strength parameter, and the slope is unstable.
In the software adopting the first judging method, the numerical calculation is not converged, a certain iteration number is usually appointed, when the calculated iteration number exceeds the appointed iteration number, the force unbalance coefficient still cannot meet the program default value, and the slope is considered to be unstable, but in the actual situation, if the iteration number is increased, the force unbalance coefficient can meet the program default value. Therefore, the magnitude of the safety coefficient depends on the designated iteration times to a certain extent, and cannot fully reflect the damage condition of the slope. In addition, the force unbalance coefficient is an artificial parameter for measuring the convergence degree in the calculation process, and can be a specific index of a numerical model along with artificial assumption, so that the randomness is high. If the model is calculated, the force unbalance coefficient can be set to be 1e-5 or 1e-7, and the smaller the force unbalance coefficient is, the more accurate the iteration convergence is. In software adopting the second judging method, when the displacement suddenly changes, the displacement obtained by calculation often exceeds the displacement in the actual engineering, and the unrealistic feeling is given to people. In the software adopting the third judging method, when the plastic yield zone is communicated, the displacement is large, and the local displacement exceeds the displacement which cannot be generated by actual engineering.
Disclosure of Invention
The invention aims to solve the problems and provides a safety factor determination method based on soil slope strength folding and subtracting.
The technical scheme of the invention is as follows: the safety coefficient determination method based on the soil slope strength folding and subtracting method comprises the following steps:
s1: collecting the intensity parameters of the soil slope, and calculating the maximum slope displacement and the maximum slope strain;
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 soil slope strength parameters according to a set proportion, calculating the corresponding slope displacement and slope strain according to the reduced strength parameters, and determining the maximum slope displacement S max And maximum slope strain epsilon max 。
Further, in step S1, the maximum slope displacement S max The relation of (2) is:
wherein F (·) represents a side slope displacement function, F s Represents the safety coefficient, c represents the cohesive force of the soil body,
the internal friction angle of the soil body is represented, and E represents the modulus of the soil body;
maximum slope strain ε max The relation of (2) is:
wherein f' (. Cndot.) represents the slope strain function.
Further, the methodIn step S2, the specific method for determining the safety factor is as follows: based on the maximum slope displacement and the maximum slope strain, drawing a curve by taking the reduction coefficient as a horizontal axis and the slope displacement or the slope strain as a vertical axis, wherein in the curve, the reduced strength parameter is positioned at the maximum slope strain epsilon max And determining 15% of the slope as a broken state, and determining the safety coefficient of the slope according to the previous stage strength parameter.
Further, in step S2, the cohesive force c corresponding to the n-level strength parameter during slope failure n And internal friction angle
The calculation formulas of (a) are respectively as follows:
c n ＝c(1-f)
wherein f represents a reduction coefficient, c represents a cohesive force of the soil body,
representing the internal friction angle of the soil body.
The beneficial effects of the invention are as follows: the invention overcomes the defects of inaccurate calculation and larger error of the traditional strength folding and subtracting method, takes the maximum shearing strain reaching 15-20% as the instability index for judging 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 maximum shear strain is typically 15% as the failure point.
Drawings
FIG. 1 is a flow chart of a safety factor determination method based on soil slope strength folding and subtracting;
FIG. 2 is a schematic diagram of displacement and shear strain for each condition.
Detailed Description
Embodiments of the present invention are further described below with reference to the accompanying drawings.
As shown in FIG. 1, the invention provides a safety factor determination method based on soil slope strength folding and subtracting, which comprises the following steps:
s1: collecting the intensity parameters of the soil slope, and calculating the maximum slope displacement and the maximum slope strain;
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 soil slope strength parameters according to a set proportion, calculating the corresponding slope displacement and slope strain according to the reduced strength parameters, and determining the maximum slope displacement S max And maximum slope strain epsilon max 。
In the embodiment of the present invention, in step S1, the maximum slope displacement S max The relation of (2) is:
wherein F (·) represents a side slope displacement function, F s Represents the safety coefficient, c represents the cohesive force of the soil body,
the internal friction angle of the soil body is represented, and E represents the modulus of the soil body;
maximum slope strain ε max The relation of (2) is:
wherein f' (. Cndot.) represents the slope strain function.
In the embodiment of the present invention, in step S2, the specific method for determining the security coefficient is as follows: based on the maximum slope displacement and the maximum slope strain, drawing a curve by taking the reduction coefficient as a horizontal axis and the slope displacement or the slope strain as a vertical axis, wherein in the curve, the reduced strength parameter is positioned at the maximum slope strain epsilon max 15% of the edges of (2)And determining the slope as a damage state, and determining the safety coefficient of the slope according to the previous stage strength parameter. It is considered that the maximum strain of 15% or more is considered to reach the failure state. The corresponding in-line number is taken as the intensity.
In the embodiment of the invention, in step S2, the cohesive force c corresponding to the n-level strength parameter during slope damage n And internal friction angle
The calculation formulas of (a) are respectively as follows:
c n ＝c(1-f)
wherein f represents a reduction coefficient, c represents a cohesive force of the soil body,
representing the internal friction angle of the soil body.
The technical scheme of the invention is described below with reference to specific embodiments.
In the specific calculation of the reduction coefficient, for convenience of explanation, the calculation of each level of reduction is referred to as a working condition, that is, the working condition one in the initial calculation, and so on. According to the reduction calculation method provided by the invention, the initial strength parameter is taken as a working condition 1, the strength parameter is reduced according to a reduction coefficient method, calculation is performed under different working conditions, the slope angle 45-degree slope three-dimensional model is not converged in working condition 6, the displacement and strain calculation result values of working conditions 1 to 5 are shown in table 1, and the change trend of the displacement maximum value and the shear strain maximum value increasing with the reduction coefficient is shown in fig. 2.
TABLE 1
It can be seen that the maximum displacement for condition 4 (point B in fig. 2) is increased by 0.08m compared to condition 3 (point a in fig. 2), the maximum shear strainThe maximum value of the displacement of the working condition 5 (point C in the figure 2) is increased by 7.0%, compared with the working condition 4, the maximum value of the shear strain is increased by 0.18m, the maximum value of the shear strain is increased by 41.6%, the displacement and the strain value of the working condition 5 (point C in the figure 2) are suddenly changed, and the shear strain of the working condition 5 (point C in the figure 2) reaches 54.30%, which indicates that the soil body is in a plastic state at the moment, the soil body is damaged, and the slope is unstable. Thus, condition 4 (point B in FIG. 2) is determined to be the critical failure point, corresponding to F s Is a safety factor.
The working principle and the working 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 slope, when the maximum shear strain at a certain place is greater than 15%, the limit equilibrium state is reached, which means that the slope has reached the slow limit equilibrium state, and the slope is unstable. However, since the maximum shear strain calculated during calculation is not just 15%, but a value of more than 15%, a range of 15 to 20% of the maximum shear strain is selected as a method for determining the slope destabilization.
The beneficial effects of the invention are as follows: the invention overcomes the defects of inaccurate calculation and larger error of the traditional strength folding and subtracting method, takes the maximum shearing strain reaching 15-20% as the instability index for judging 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.
Those of ordinary skill in the art will recognize that the embodiments described herein are for the purpose of aiding the reader in understanding the principles of the present invention and should be understood that the scope of the invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific modifications and combinations from the teachings of the present disclosure without departing from the spirit thereof, and such modifications and combinations remain within the scope of the present disclosure.
Claims (3)
1. The safety coefficient determination method based on the soil slope strength folding and subtracting method is characterized by comprising the following steps of:
s1: collecting the intensity parameters of the soil slope, and calculating the maximum slope displacement and the maximum slope strain;
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 soil slope strength parameters according to a set proportion, calculating the corresponding slope displacement and slope strain according to the reduced strength parameters, and determining the maximum slope displacement S max And maximum slope strain epsilon max ；
S2: determining the safety coefficient of the soil slope according to the maximum slope displacement and the maximum slope strain of the slope;
in the step S2, the specific method for determining the safety coefficient is as follows: based on the maximum slope displacement and the maximum slope strain, drawing a curve by taking the reduction coefficient as a horizontal axis and the slope displacement or the slope strain as a vertical axis, wherein in the curve, the reduced strength parameter is positioned at the maximum slope strain epsilon max And determining 15% of the slope as a damaged state, determining the safety coefficient of the slope according to the previous stage strength parameter, selecting a range of 15-20% of the maximum shear strain as a judgment slope instability, and taking the corresponding stage number as strength.
2. The method for determining a safety factor based on soil slope strength folding and subtracting as claimed in claim 1, wherein in said step S1, the maximum slope displacement S max The relation of (2) is:
wherein F (·) represents a side slope displacement function, F s Represents the safety coefficient, c represents the cohesive force of the soil body,
the internal friction angle of the soil body is represented, and E represents the modulus of the soil body;
maximum slope strain ε max The relation of (2) is:
wherein f' (. Cndot.) represents the slope strain function.
3. The method for determining safety coefficient based on soil slope strength folding and subtracting as claimed in claim 2, wherein in said step S2, said cohesive force c corresponding to n-level strength parameter at slope breaking n And internal friction angle
The calculation formulas of (a) are respectively as follows:
c n ＝c(1-f)
wherein f represents a reduction coefficient, c represents a cohesive force of the soil body,
representing the internal friction angle of the soil body. />
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