Study On Failure Mechanism And Early Warning Criterion Of Excavated Loess Slope

In recent years,with the development of the loess plateau region,the construction of the region has been increasing.The resulting geological disasters are also increasing.The loess landslide that induced by human engineering activity showed a sharp upward trend.The scale of sliding is getting bigger and bigger,and the loss is more and more serious.The harm of loess landslide that induced by excavation is relatively heavy.Besides,the process of formation and evolution is not easy to observe,that is concealed and hysteresis.If the loess slope excavation leads to the destruction of the slope,it will cause serious consequences.Therefore,it is very important to study the excavation of loess slope.This paper takes the Shajingyi landslide of Lanzhou that is the typical excavation of loess landslide as the research object.Collecting and investigating the geologic environment background of the study area.And detailed investigation of the landslide.The triaxial test under different stress paths,the numerical simulation analysis after generalized profile,the physical simulation test of loess slope excavation and the three-dimensional numerical simulation are used to study the excavation of loess slope.The model is combined with the slope prototype.According to the basic characteristics of slope deformation,the penetration of plastic zone,the development of slope crack,the characteristics of deformation curve of monitoring point and the change of safety factor,establish the dynamic prediction system for deformation and failure of excavated loess slope.The main research results are as follows:(1)Shajingyi landslide is a large traction type,the accumulation layer-bedrock contact surface landslide.A large number of cracks are developed on the slope,and the slope is cut into strips and blocks,resulting in poor slope integrity.(2)The slope is mainly composed of particles with uneven grain and good gradation.The c and ? values of undisturbed soil samples and remolded soil samples at different water contents were measured by direct shear test.It is found that the structure of the original loess sample is better.And which contains other components of impurities,resulting in the mechanical parameters of the two soils are different when the conditions are basically the same.(3)Through the triaxial tests under different stress paths,it is found that the required loads under the RTC path are less than the CTC path under the same conditions.In short,the soil is more prone to damage under unloaded triaxial test.During the test,the two stress paths are equivalent to the increase in partial stress.But the conventional triaxial test shear process of constant pressure,axial pressure is increasing.Leading to more loads borne by the water between the soil particles.In the unloading triaxial test,the confining pressure is decreasing.The water between the soil particles is less loaded.Therefore,under the same conditions,the pore water pressure ratio under the RTC path is smaller than the CTC path.(4)There are many factors that affect the slope stability.Through the numerical simulation,it is found that the higher of the excavation rate,the bigger of the slope angle,the worse the slope stability.Through the three-dimensional numerical simulation,with the excavation,the slope deformation and shear strain increment are increasing,the stress concentration is more and more obvious,the stability of the slope gradually reduced.Finally,the shear strain increment occurs,the factor of safety is less than 1,the slope deformation is increasing and the slope is destroyed.(5)Through the physical simulation test of excavating loess slope,the process of excavation loess slope instability is as follows:slope stability?small loess falls?the rear part of the slope produces tension cracks?the original cracks are extended and new cracks are created?the cracks on the rear slope are basically through ?cracks pass through,the rear of the slope to form a similar "ring chair"landslide wall.(6)According to the deformation and failure characteristics of excavated loess slope,the physical simulation test of excavated loess slope,it is combined with the original slope to obtain the slope stability criterion,tangential angle criterion,velocity and acceleration criterion,and the penetration rate of plastic zone.In addition,constructing the dynamic prediction system for excavation slope deformation.The study shows that the tangential angle is greater than 86° and the plastic zone is basically penetrated as the failure criterion of excavated loess slope.