Study On Stability Analysis And Evaluation Of Loess Slope Based On Seepage Theory

China is the country with the widest distribution of loess in the world.Loess landslides are common in the steep slopes of loess,especially in heavy rain or in continuous rainfall conditions,which are easy to cause landslide geological disasters,which seriously threaten people's lives and property.Therefore,in this paper,the stability of loess slope will be studied based on saturated-unsaturated seepage theory under rainfall conditions,especially the study of seepage field distribution in loess has reference value and practical significance for the stability of loess slope,prevention measures,disaster prevention and also mitigation projects.Based on saturated-unsaturated seepage theory and unsaturated transient governing equation,considering the influence of rainfall intensity,rainfall time,saturated permeability coefficient and anisotropy on the stability of loess slope,with the use of GeoStudio software,the seepage stability of loess slope is detailedly studied.The SEEP/W module is used to calculate the transient seepage field at different time points on the observation sectionO-O₁ of the loess slope.The distribution of pore water pressure and volumetric water content with elevation is obtained,and the propulsion rate of the wetting front and the elevation of the groundwater level are analyzed.Taking the results of pore water pressure as the initial condition of calculation with SLOPE/W module,the law of variation of safety factor of loess slope with time is summarized,and the stability of loess slope is evaluated objectively and practically.This paper has the following conclusions:?1?When the rainfall intensity is less than or equal to the permeability coefficient,the surface runoff does not form atmospheric rainfall,mainly infiltrates into the soil.Therefore,the pore water pressure and volumetric water content in the soil have great change with the increase of rainfall intensity,and have great influence on the stability coefficient of loess slope.When the rainfall intensity is greater than the permeability coefficient,most of the rainfall is discharged by surface runoff.Only a small part of the rainfall infiltrates into the slope soil.Therefore,the change of pore water pressure and water content in the soil are not obvious with the increase of rainfall intensity,so it has little influence on the safety factor of loess slope.?2?When the rainfall intensity remains unchanged,with the increase of rainfall duration,the rise of groundwater level in the front edge of loess slope,the infiltration depth and the volume moisture content of soil in loess slope all increase.The suction of matrix decreases,which leads to the decrease of shear strength of soil in loess slope.The final result is a decrease in the safety factor.In the range of 48 hours of rainfall duration,the reduction of the safety factor varies linearly with the increase of rainfall duration.?3?Under the condition of keeping the rainfall intensity and rainfall duration constant,the larger the saturated permeability coefficient,the easier the rainwater enters the shallow layer of the slope,so that it is closer to saturation,and the matrix suction of the loess decreases faster.As a result,the corresponding safety factor decreases faster.On the contrary,the smaller the saturated permeability coefficient is,the rainwater is more difficult to penetrate into the interior of the loess slope,it makes the influence of rainfall on the volumetric water content and the matrix suction in the loess slope small,so the safety factor of the loess slope reduces slowly.When the saturated permeability coefficient exceeds the rainfall intensity,the magnitude of the change in the safety factor decreases.?4?Keeping the external rainfall conditions constant,and remaining the horizontal permeability coefficient unchanged,as the vertical permeability coefficient increases,that is,as the Ky/Kx increases,the rate of decrease of the safety factor of the loess slope increases.At the same time,the recovery rate is also increasing,but when Ky/Kx is greater than 5,the influence of the anisotropy of the permeability coefficient on the stability of the loess slope is almost unchanged.?5?Using the limit equilibrium method to analyze the stability of the 2-2 section of the Tongchuan loess slope,the calculation results are consistent with the influence of rainfall intensity on the seepage stability of the loess slope,which verifies the above rule.Based on the seepage theory,it is reasonable to use GeoStudio software to calculate and analyze the seepage stability of loess slope.This method can be applied to solve the problem of seepage stability analysis of the same type of loess slope.?6?Using the finite element and limit equilibrium method to analyze and calculate the stability of loess slope,the calculation result is smaller than the safety factor calculated by the limit equilibrium method alone,indicating that the use of the limit equilibrium method is dangerous.It is suggested that the combined finite element method and limit equilibrium method should be used to analyze the stability of loess slope under rainfall condition in later researches.