Model Test Study On The Whole Process Of Rainfall Induced Loess Landslide

The Loess Plateau,with a population of about 100 million people,is fragmented with fragile geological environment.Frequent natural disasters such as landslides,collapses,and ground subsidences cause heavy casualties and property losses,restricting economic development.More than 90%of the landslides are induced by rainfall.Water weakens cementation,increases self-weight,expands fissures,and reduces strength influencing the stability of slope.A model test of rainfall-induced landslide was carried out to study the infiltration and migration of water and failure process of slope,which can improve the theory of loess disasters and has important value for disaster prevention and mitigation.Take Baqiao landslide as a research prototype which occured in september 17^th,2011.Geological background was learned through on-site investigation.Laboratory tests were performed to get physical and mechanical parameters of the soil.A landslide experiment was conducted to monitor and observe the failure process.Numerical simulation studies the response time and spatial-temporal distribution of soil properties of original slope under rainfall conditions.Through time-history analysis of moisture,pore water pressure,stress and other micro-indicators,summarized the macro phenomena such as surface fissures and joint opening.Failure process is discussed from the perspective of both phase characteristics and mechanical mechanisms.Conclusions are as follows:（1）The curve of soil volumetric water content and pore water pressure versus time is nearly S-shaped during the whole process.Increasing rate is low at the begining and ending,and relatively high near the landslides happened.Both response time and changing level are inversely proportional to depth.Slope surface responded fast with strong fluctuation,but reaction in depth was slow and slight.Joints have significant influence on accelerating water infiltration.（2）Distant from the joint,the curve of vertical stress versus time is nearly Inverted S-shaped.Vertical stress increased slightly due to the compaction of soil at the beginning and ending,and decreased greatly due to the internal displacement near the landslides happened.Near the joint,vertical stress growed steadily.Surface fissures undergo the process of expansion→erosion→filling.Topological characteristics rised first then falled.（3）The whole failure process of landslide is divided into three stages by time:weight gaining,softening and deforming,stabilizing.Volumetric water content was about 23%when landslides happened.Pore water pressure increased 2～3 k Pa.Vertical stress decreased nearly 7k Pa.Maximum joint opening was 48mm.Overall displacement of the slope was more than 5cm.Driping and leaching effect caused expansion of fissures,meanwhile changing in matric suction and pore water pressure affected shear resistance of the soil.（4）Transient seepage simulation and stability analysis revealed the difference in the infiltration rate of water in different depth,with or without joints,as well as spatial and temporal distribution of both horizontal and vertical displacement and maximum shear strain.Low permeability of the paleosol layer led to its volumetric water content and pore water pressure being higher than loess layer,making their interface a weak surface during the landslide.