Study On Stability Evaluation And Protective Measures Of Abandoned Loess Cave Slopes In Bailu Plateau

This article takes the abandoned loess cave slope of Sipo Village,Mingdu Street,Chang’an District,Bailu Plateau as the research object,through a detailed field investigation to study the deformation and destruction characteristics of the abandoned loess cave,and summarizes the destruction mode of the abandoned cave;Using laboratory experiments to study the physical and mechanical properties of loess and paleosol,and analyze the changing law of water content and soil mechanical properties in different cave states such as normal residence and cave dwelling;with the help of MADIS GTS NX finite element software to simulate cave slopes under different cave states.Furthermore,the mechanism of deformation and failure of abandoned loess cave slopes is revealed and corresponding prevention measures are proposed.The research results obtained are as follows:（1）The landform type of the study area is loess terrace,and the slope shape is stepped.Cave failure types include:cracks,cave collapses and cave collapses.Influencing factors of stability include:topography,material composition,hydrology,human activities and rainfall.The failure modes in the study area can be divided into cave roof failure and cave collapse failure.（2）Summarize the difference between the physical and mechanical properties of Q₂^eolloess and paleosol through laboratory tests on the soil samples in the study area;Through the direct shear experiment in the laboratory,the water content and mechanical properties of the soil in different cave states are obtained as follows:With the increase of water content,the cohesive force c of Q₂^eol loess and ancient soil decreases with the increase of water contentω,and the change trend is an exponential function relationship;The internal friction angleφdecreases with the increase of the water contentω,and the change trend is a quadratic polynomial relationship.（3）The strength reduction method（SRM method）is used to analyze the stability of the cave slope,and the slope stability gradually decreases with the increase of water content.Among them,the stability of the abandoned loess cave slope is significantly lower than that of the normal residence cave.（4）Through the analysis of the numerical simulation results,it is found that the maximum vertical displacement of the soil around the cave appears in the vault of the cave;the maximum horizontal displacement occurs at the midpoint of the vertical wall of the cave adjacent to the two caves;the vault,bottom and vertical wall of the cave The stress is large,and the stress concentration phenomenon occurs at the non-smooth corner;the plastic zone first appears near the midpoint of the straight arm adjacent to the two caves,and the equivalent plastic strain value of the regional soil between the two caves is significantly greater than that of other regions..With the change of the state of the cave,that is,the water content of the slope body continues to increase,the stress and strain values continue to increase,and each plastic strain zone has a tendency to expand toward the top of the slope and the interior of the slope body.The possibility of overall instability in the slope of the loess cave is increased.（5）The analysis and summary of the MADIS numerical simulation results of the cave slopes in different states show that the failure mechanism of the abandoned loess cave slope is:as the cave is abandoned,the increase of the soil moisture content leads to the decrease of the mechanical properties of the soil and the loss of the local free surface soil With the effect of rainfall and other factors,the mechanical properties of the soil are further reduced,and the arch structure of the cave is destroyed,which causes the collapse of the slope where the cave is located and other overall failure.（6）Drawing on the existing prevention measures of abandoned loess cave slopes and combining with the destruction mechanism of abandoned loess cave slopes in the study area,the treatment engineering design of abandoned loess cave slopes is carried out,and numerical simulation software is used to compare and analyze the slopes before and after treatment.