Seismic Subsidence Evaluation Of Loess Sites Under Strong Earthquakes

Many studies show that loess is sensitive to ground motion because of its special structure.Loess is widely distributed in our country,and it is very indispensable to study the seismic subsidence property of loess,which is closely related to the engineering construction in loess area,and is of great significance for the prediction and prevention of seismic subsidence disaster.Based on the project of Fuping earthquake plot,this paper studies the seismic subsidence of Loess by using TYS-20 micro-computer controlled electro-hydraulic servo soil dynamic triaxial testing machine of the Geotechnical Engineering Open Research Laboratory of the Ministry of land and resources of Chang'an University.Firstly,the topography,lithology,geological structure,seismic activity and other aspects of Fuping County are comprehensively analyzed,and the engineering properties of loess in the study area are analyzed and studied through routine geotechnical tests.On this basis,the dynamic shear modulus ratio(G_d/G_d0),damping ratio(?)and shear strain(?)of representative loess strata are obtained by triaxial test of undisturbed loess.The seismic subsidence properties of undisturbed loess in different depths and geomorphic units are studied,and the seismic subsidence curve is quantitatively analyzed,and the subsection function mathematical model is established.The results show that the seismic subsidence curves of loess with different depths(5m,10m,15m)have similar change rules,and the typical seismic subsidence curves display those three periods:initial deformation,curve deformation and shear deformation;loess with different geomorphic units has different seismic subsidence characteristics.Secondly,FLAC3D is used to build the three-dimensional site model of typical points,and the numerical simulation analysis of the Loess Site subsidence under the strong earthquake action is carried out.The vertical displacement change rule of the site under the horizontal earthquake action of different exceedance probability is obtained,and the final subsidence is 2.467cm and 6.167cm respectively.Finally,based on the layered summation method,the seismic subsidence of loess site under strong earthquake is evaluated and compared with the numerical simulation results.The evaluation results are as follows:under the condition of 10%exceedance probability in 50years,the slight and medium loess seismic subsidence areas are distributed on the Loess Plateau and the second terrace of Weihe River;under the condition of 2%exceedance probability in 50 years,the slight and medium seismic subsidence areas are mainly distributed on the Loess Plateau,and the serious seismic subsidence areas are mainly distributed on the Loess Plateau,the second terrace of Weihe River and the third to fourth terrace of shichuanhe river.Therefore,for the existing buildings and new buildings on the site that may have earthquake subsidence disaster,the damage caused by the earthquake subsidence of loess should be properly considered.Attention should be paid to this part of potential earthquake geological disaster in the design of foundation and foundation.