Stability Analysis Of Typical Loess Tableland Landslide Under Cave Development Environment

As a unique landform in the Loess Plateau,the occurrence of loess caves is closely related to the characteristics of landslides,and the development and evolution of the caves are affected by soil properties,stratigraphic structure and other factors.In this paper,based on field investigation,a typical section is selected for indoor and outdoor experiments on Loess Landslides Induced by loess caves.The physical and mechanical properties,groundwater characteristics,loess microstructure and soil water characteristic curve of soil in cave area and non-cave area are compared and analyzed.Finally,the influence of rainfall and loess cave on landslide stability is analyzed by numerical simulation.The main conclusions are as follows:(1)Based on the study of the physical and mechanical properties of Beiguo landslide,the following conclusions are drawn: the bulk density and shear strength of the soil in the cave area of the Beiguo landslide are greater than that of the non-loess cave area,and the porosity is less than that of the non-loess cave area.The slip zone soil has the largest bulk density,the smallest porosity,and the lowest shear strength.Shortly after the landslide occurred,the landslide soil in a disturbed state and the parameters of the soil are not stable.The soil properties of the cave area are stable due to the long deposition time.The parameters of the soil of the slip zone are quite different from the first two.The microstructure of loess shows that the depositional environment of landslide soil is simple and the source is single;the soil is mostly coarse silty soil with low clay content,which is conducive to the collapse of soil and provides a good environment for the development of caves.(2)The saturated hydraulic conductivity of the study area is 0.2mm/min-1.3mm/min.The permeability coefficient of the soil on the back edge of the landslide(cave area)is less than the that of the landslide soil(non-cave area),and the porosity rate is the main factor affecting infiltration;at the back edge of the landslide,the permeability coefficient of loess caves is smaller than that of the farmland,and organic matter is the main factor affecting the infiltration.(3)The geophysical exploration results of the electrical instrument show that the resistivity of the cave area at the back edge of the landslide is high,and there are cavities in the underground area;the groundwater in the farmland area moves towards the landslide direction;the loess cave development is the long-term indirect cause of the landslide instability,and the groundwater uplift caused by agricultural irrigation is the short-term direct cause of the landslide.(4)Stability simulation results of the Beiguo landslide under different rainfall conditions: Under the conditions of light rain,moderate rain and heavy rain,the changes of volume moisture content and pore water pressure are concentrated on the slope surface.With the increase of rainfall duration,the water content of the slope surface increases gradually,and the pore water pressure decreases gradually;In the initial state,the safety factor of Beiguo landslide is 0.910,which is unstable;in the light rain and moderate rain conditions,the safety factor of the landslide decreases very little,heavy rain has a great impact on the stability of the landslide,and the stability of the landslide decreases by 0.014,when the rainfall duration increases to 7d,the water content of the surface soil is the same as that of the groundwater level;when the rainfall duration is 1D,2D and 3D,the water content of the landslide is the same The safety factor decreased by 0.028,0.047 and 0.093 respectively.It shows that with the increase of rainfall duration,the safety factor of landslide decreases faster and faster.(5)The stability of Beiguo landslide under cave environment is discussed by Midas GTS numerical simulation software.Single cave has no effect on the stability of the landslide basically.In the case of two or four caves,the stability coefficient of the slope decreases greatly.The more caves there are,the worse the slope stability is;the closer the caves are to the edge of the tableland,the worse the slope stability is.The main factors affecting the formation of caves are the condition of porosity,the action of water and the dominant channel of joint and fissure formation.