Static Stability And Seismic Dynamic Response Of Unstable Loess Slope In Zhongzhuanggou,Xining City

Loess is widely distributed in Xining Basin in the northeast region of Qinghai-Tibet Plateau.Due to the specific geomorphic conditions,climatic conditions,environmental geological conditions,the intensification of seismic activities and human engineering activities,slope disasters occur frequently in the loess area,causing great losses to people’s lives and property.Therefore,it is of great significance to study the static stability and seismic dynamic response of unstable loess slopes in this area.Taking Zhongzhuanggou loess unstable slope in Xining City as an example,based on field investigation,laboratory test and field in-situ test,aided by InSAR surface deformation analysis and using numerical simulation as the main means,this paper firstly conducted a preliminary study on the overall characteristics and local deformation characteristics of the unstable slope through field investigation.Meanwhile,the surface deformation characteristics of the unstable slope in recent 5 years were analyzed by SBAS-InSAR technique.Secondly,GEO-Studio and FLAC^3D are used to analyze the static stability of unstable slopes.Finally,on the basis of static conditions,the characteristics of seismic dynamic response of unstable slopes are studied by selecting typical ground motion data,and the changes of unbalance force,acceleration,displacement and stress-strain of unstable slopes under earthquake are analyzed.The research results obtained are as follows:1)Through field investigation and data collection,the basic characteristics of loess unstable slope in the study area are revealed.The overall slope of loess unstable slope is steep.There are four obvious deformation areas in the slope,one at the slope surface and three at the foot of the slope.The deformation occurred on the slope was caused by the collapse of the tunnel chamber during the excavation and construction of diversion tunnel.A collapse pit with diameter of 10.5m and depth of 16m was formed.There are 3deformations at the foot of the slope,among which 2 deformation areas have collapsed,and 1 platform crack at the front of the deformation area is currently accelerating tensile deformation and may collapse at any time.Through field investigation,the slope is in a stable state.2)Through laboratory physical and mechanical tests,the basic laws of the physical properties,hydraulic properties and mechanical properties of the loess in the study area were studied.The experimental results show that the collapsibility of loess in the loess field in the study area ranges from grade II to grade IV,and the collapsibility of loess decreases with the increase of the buried depth of soil samples.Dry density and natural water content increase with the increase of buried depth.The pore ratio and porosity of loess decrease with the increase of depth.The compressibility of loess increases with the increase of pore ratio.3)Based on the analysis of surface deformation of the unstable slope by SBAS-InSAR,it is concluded that the main displacement of the unstable slope of loess occurs in the middle and northeast side of the slope,and the maximum displacement is-11.2mm/a.By analyzing the deformation characteristics of the study area through the time series curve,it was found that the deformation trend of the loess unstable slope occurred in August 2020,and combined with the rainfall characteristics of the local rainfall in the past five years,the time period of the slope deformation was consistent with the time period of high rainfall in the study area.The analysis results inferred that rainfall was one of the main causes of slope deformation.4)The static stability of the unstable slope was evaluated.GEO-Studio and FLAC^3Dwere used to analyze the stress-strain,deformation and plastic zone of the unstable slope in loess.The results showed that the local slope was in an understable or basically stable state,and the deformation mainly occurred in the middle and northeast side of the slope.It is basically consistent with the main deformation area of InSAR surface deformation analysis results.5)The seismic dynamic response analysis of the unstable slope was carried out.On the basis of static stability analysis,GEO-Studio,FLAC3D and other numerical simulation methods were used to apply seismic loads to the slope by selecting recent typical ground motion data near the study area.The characteristics of maximum unbalance force,acceleration,displacement and stress-strain response of unstable slope under earthquake are analyzed.The results show that the slope stability under seismic action is worse than that under static action.The slope is in a local understable state under seismic action,and the maximum displacement is 7.52 cm.The deformation area mainly occurs in the middle and northeast side of the slope,and the deformation range is larger than that under static action.With the increase of earthquake time,the deformation of unstable slope becomes larger.By setting up monitoring points on the top,surface and foot of the slope,the acceleration characteristics of the slope show that the acceleration amplitude of the soil at the top of the slope is greater than that at other positions.