Research On Dynamic Response Characteristics And Failure Mechanism Of Slopes With Overburden Layer Under Earthquake

China faces severe earthquake and landslide disaster.In nature,slopes with overburden layer are widespread,and landslide disasters are prone to occur under earthquakes.The study of slope dynamic response is the foundation of the slope anti-seismic design.In this paper,the study of seismic dynamic response of slopes with overburdens has been carried out to provide reference for the protection and treatment of slopes with overburdens.Slopes with overburden are divided into three forms:slope top coverage,slope surface coverage,and slope top-slope coverage.According to the geological statistics of stations in the southwest region,the thickness of the overburden layer is determined to be 0m,2m,4m,8m,12m,16m.By establishing a large number of slope models with different thickness of overburden layers,using FLAC 3D numerical simulation method,a large number of monitoring points are arranged in the slope body to monitor the acceleration time history curve under the action of earthquake.After filtering and baseline correction,the peak acceleration(PGA)of each point is obtained,and the peak acceleration amplification factor(AAF)of the slope body is used to describe the slope response law in the time domain.Taking the foot of the slope as the base point,the PGA magnification factor of each point is calculated,and the AAF contour map on the slope profile is obtained.The influence law of the slope with different cover forms and the thickness of the cover layer on its seismic dynamic response is analyzed.For slopes with different coverage forms,the effects of terrain parameters,seismic source parameters,and soil parameters of the overburden layer on its response are analyzed.By summarizing the influence of each parameter on the response law,using the dimensional analysis method combined with elastic wave theory and statistical analysis,the critical overburden thickness of dynamic response is obtained:h_thre=(0.11?0.15)?.Through modal analysis to study the dynamic characteristics of the slope with overburden,it is found that the slope with overburden has different modal characteristics from the homogeneous slope.The slope mode of slope with overburden is more complicated.The low-order modes mainly reflect the dynamic characteristics in the overburden layer,and the mode with the largest mass score reflects the overall dynamic characteristics of the slope.Through the analysis of the dynamic characteristics of slopes,the spectrum amplification characteristics of slopes with different overburden thicknesses are studied.The slopes with different overburden forms show different resonance curves in the overburden layer.The top covered slope is mainly affected by the maximum modal frequency of mass fraction.The resonance characteristics of the slope with surface overburden or the slope with top and surface overburden are more affected by the low frequency.The influence of the thickness of the overburden on the resonance characteristics of the slope was investigated by taking top covered slope as an example.Combining the strength reduction method,the dynamic failure characteristics of the slope with overburden are studied.First,the slope strength parameters are reduced,and the slope is damaged by inputting ground motion to explore its failure characteristics.The study found that under dynamic action,the slip surface of the slope with overburden occurred in the overburden layer.Shear failure began at the foot of the slope,and then the shear failure zone gradually expanded upward,and then connected to the tensile failure zone on the top of the slope.Eventually lead to slope damage.The location of the slip surface of slopes with different overburden thickness is different.When the overburden is thinner,the location of the slip surface is affected by the interface of the subgrade and is closer to the static failure surface,and the cut out position at the slope toe is deeper.When the overburden layer is thicker,there will be two slip surfaces.The position of the shallower slip surface is close to that of the static slip surface,and the deeper slip surface is close to the interface of the base cover in the overburden.The research shows that the location of the interface between the base and overburden and the soil strength parameters of the slope have a greater impact on the location of the dynamic slip surface.