Study On Stability Of Loess Landslide Under Rainfall Conditions

Shaanxi is one of the areas where landslides and other geological disasters are more serious and frequent.Especially based on rainfall statistics in the past ten years,the rainfall in Shaanxi has moved northward,leading to an overall increase in precipitation in northern Shaanxi;moreover,rainfall is mainly concentrated in August and September,which has increased the frequency of loess landslide disasters in northern Shaanxi.This paper takes the Chengaowan landslide in Yulin City,Shaanxi Province as the research object,through detailed field investigation,combined with various geophysical prospecting results,indoor geotechnical tests,transfer coefficient method and finite element strength reduction method,the basic characteristics of the landslide?the physical and mechanical properties of loess and the stability of the landslide under different working conditions are studied.On this basis,the deformation and failure mechanism of the landslide site under the effect of continuous rainfall or heavy rain is revealed.The research results are as follows:(1)The geomorphic unit of the landslide site belongs to the slope of the loess beam,which generally presents the characteristics of steep upwards and gentle downwards;the landslide is a large-scale low-speed slow-moving loess landslide;the main body of the landslide is composed of plain fill,Malan loess,paleosol,Lishi loess and three-toed red soil;there are through cracks on the surface of the rear edge of the landslide,and there are three landslides around the sliding body;there is constant flowing water at the bottom of Yangliugou ditch,and no springs and water seepage points have been found.(2)Laboratory test results show that the basic physical parameter values of the Malan loess overlying the landslide are significantly different from the underlying three-toed red clay;the landslide loess is silt except for the three-toed red clay which is a silty clay;plain fill has slight collapsibility,and Malan loess has medium-strong collapsibility;the permeability coefficient of three-toed red clay is two orders of magnitude;in the natural state,the mechanical strength of Malan loess is the lowest,and the mechanical strength of the three-toed red soil is the highest;in the saturated state,the mechanical strength of each layer of loess is significantly reduced,and the value of the three-toed red soil is the most obvious.(3)The stability analysis results show that the landslide is in a basic stable state as a whole in its natural state,and partially in an under-stable state;under heavy rain conditions,the landslide is in an unstable state as a whole.Moreover,the numerical simulation results show that with the increase of rainfall,the stability of the landslide gradually decreases.(4)Numerical simulation results show that the maximum longitudinal displacement of the soil of the landslide site appears at the toe of the slope and the protruding area of the slope under the slope;the maximum horizontal displacement value appears on both sides of the slope body near the top of the slope;the maximum vertical displacement appears at the top of the slope and the protrusion of the middle and lower slope,which is shown as downward displacement at the top and upward displacement in the middle part of the slope.(5)Deformation and failure mechanism of landslide under continuous rainfall and strong rain: continuous rainfall or heavy rain runoff on the surface,which scours the slope to form a mud flow and causes the slope to break,providing a channel for rainfall to infiltrate into the slope;rainfall infiltrates into the slope through sinkholes or cracks,and stays on the red clay layer with poor permeability,softening and argillizing the loess at the interface,resulting in the reduction of the effective normal stress and shear strength of the soil;in addition,rainfall will promote the development and expansion of existing cracks.When the cracks develop to make the undamaged area reach the critical value,the landslide will lose its overall stability and form landslide disaster.