Dynamic Response Characteristics And Stability Analysis Of Loess Slope Under Strong Earthquake

The porous and weak cementation characteristics of Loess and the high-risk seismicity in Loess Plateau lead to the development of seismic Loess landslide hazards which caused great casualties and property losses in this area. Therefore, further study of typical Loess slope dynamic response characteristics and stability under strong earthquakes has urgent practical and scientific significance for improving the prevention and governance capability of landslide and guiding the rational planning of urban sites in Loess Plateau.In this paper, seismic instability mechanism, dynamic response characteristics and stability of landslides in loess layer and Loess-Red beds interface landslides were analyzed by using site survey, laboratory soil test, mechanics theoretical analysis, numerical simulation and large-scale shaking table test. The main work and conclusions of research are summarized as follows:(1) Field suvey was carried out on four seismic Loess landslides of two typical types including Fenghuangzui landslide induced by Huaxian earthquake, Gedagou landslide induced by Yongdeng earthquake, Pangwan landslide and Sunjiagou landslide induced by Haiyuan earthquake. Through topographic surveying, aerial drones, shear wave velocity test and transient surface wave exploration, the instability and failure characteristics of typical loess slope were summarized, the soil types and site category were distinguished.(2) Physical and mechanical parameters of soil samples of Fenghuangzui, Gedagou and Pangwan landslide were measured by laboratory soil test. The results of density and elastic modulus of landslide soil sample are in accordance with the spatial distribution characteristics of Aeolian Loess. However, the moisture content of soil is low, the pore ratio is larger and the friction angle is smaller than the average level of the region. These abnormal phenomenon may be the intrinsic reason for the instability of the slope under strong earthquakes.(3) Based on stress analysis, the magnitude and variation trend of shear stress of slope soil in different positions during the process of slope instability under earthquake are calculated. By combing with the instability characteristics and experiment results, the seismic instability mechanisms of two typical landslides are put forward.(4) By using finite element numerical simulation method and modeling with Fenghuangzui landslide and Pangwan landslide which represent landslides in Loess layer and Loess-Red beds interface respectively, dynamic time history analysis was carried out. Form which calculation results, the dynamic response characteristics and stability of slope under strong earthquakes are obtained, and the seismic slope instability mechanisms are verified.(5) By establishing the relation between the seismic instability mechanism and the stability analysis method of Loess slope, the finite element strength reduction method is improved to reflect the seismic instability mechanism. Compared with the original method, dynamic safety factor of the improved method is more close to the result calculated by the limit equilibrium method, which ensures the rationality of improved method and verifies the seismic slope instability mechanism at the same time.(7) By conducting the typical Loess-Red beds interface slope shaking table test, the instability evolution process of such slopes is simulated under strong earthquakes. The instability characteristics of slope model and observation results of acceleration and soil pressure are all effective to verify the typical loess slope seismic instability mechanism proposed in this paper.