Seismic Subsidence Mechanism And Evaluation Method Of Unsaturated Loess

The mechanism and evaluation method of seismic subsidence of loess site under earthquake are scientific and technical problems to prevent and reduce seismic subsidence of loess site from the perspectives of seismic engineering,soil dynamics and kinematics.In this study,the field aerial survey,borehole exploration,soil-water characteristics test,dynamic triaxial test,meso-structure test,shaking table test,numerical simulation and seismic response analysis were used to select typical thick cover(filled)loess tableland sites and tableland edge and beam edge slope sites in Longdong and Longxi.This paper carries out a systematic study from the following aspects,mainly including: The influence law of loess soil condition on seismic subsidence,the characteristics of ground motion propagation in loess site,the characteristics of seismic dynamic response of unsaturated loess site,the mechanism of seismic subsidence of unsaturated loess considering soil stress conditions,the mechanism of seismic landslide subsidence of unsaturated loess,and the evaluation method of seismic subsidence of loess field based on seismic response analysis.This study comprehensively considers the influence of soil properties,static conditions,dynamic conditions and seismic wave propagation characteristics,and reveals the earthquake subsidence disaster mechanism and earthquake subsidence evaluation method.The research results can provide theoretical reference for major engineering construction and the promotion of "resilient urban and rural areas".(1)This study established a thick covering of the loess tableland sites,typical tableland edge and beam edge slope sites geological model.The influence rule of soil and water characteristics of typical loess on its seismic collapsibility is revealed.The relationship between matric suction and volumetric water content of unsaturated loess in seismic subsidence area was established.Considering the influence of physical parameters,the loess with large initial matric suction is more prone to earthquake subsidence.(2)Considering the factors of loess layer thickness and epicenter distance,the effects of loess layer thickness and epicenter distance on the seismic response of loess site under seismic load were summarized,and the relationship between seismic subsidence disaster and earthquake intensity in loess area was determined.(3)The response characteristics of homogeneous loess sites under different seismic loads were studied by shaking table tests of thickly covered loess sites.The macroscopic effect,mechanical mechanism and physical process of soil layer structure on dynamic response of loess sites were analyzed,and the influence of soil layer structure on loess seismicity was revealed.(4)Large undisturbed loess test blocks were prepared.Innovative research and development of the test block can apply the surrounding pressure device.Shaking table tests of undisturbed and filled test blocks at different depths were carried out.The influence rule,response characteristics and failure mode of static conditions on seismic subsidence of loess under different spectral characteristics and different amplitude seismic loads were studied.The mechanism of loess subsidence was revealed,the loess subsidence under different spectral characteristics and different amplitude seismic loads was tested and analyzed,and the mechanism of earthquake subsidence was explained.(5)Through different seismic force under the action of earthquake simulation shaking table tests of loess slope model,obtained the unsaturated loess earthquake macroscopic damage process of landslide,using discrete element numerical analysis,from the slope,reveals the unsaturated loess seismic landslide macro-microscopic damage characteristics,the settlement of startup mechanism and kinematics characteristics of the mechanism.(6)Considering the properties of loess,the thickness of overburden,the propagation characteristics of loess site and the seismic force,the reduction coefficient of dynamic shear stress in the mainstream evaluation method of seismic subsidence was modified.The viscoelastic shear layer method was used to analyze the seismic response of loess sites with typical thick cover.The seismic subsidence evaluation of loess field was carried out and the seismic subsidence evaluation method of unsaturated loess was obtained.