Study On Analysis Method For Spectrum Of Seismic Landslide

In our country, earthquakes frequently occur, meanwhile, a large number of mountains exist, so mountain landslides induced by earthquake often occur. The destructive power of landslide is great, and generally poses a great threat to the safety of life and property of people in mountain area. In this paper, we mainly study the resonance effect of the seismic landslide. Then based on the modal analysis theory, a new method to evaluate the safety of seismic landslide (Analysis of Seismic Landslide Spectrum, ASLS for short) is proposed. The main research contents are as follows:Base on the classical 3D Delaunay algorithm, an algorithm for 3D constrained Delaunay triangulation mesh generation is studied. The boundary of entity is described by the combo consisted of point, line and surface. And by restoring the constrained boundary and removing the local degeneracies, the consistency of solid boundary and the uniqueness of mesh can be guaranteed. In this way, the constrained Delaunay tetrahedral mesh can be effectively generated for any complex 3D solids with constraints. By using any tetrahedral mesh generation method, some low-quality elements may be generated, and according to this problem, the paper presents quality parameters and its calculation method, that is by controlling the magnitude of the ratio of circumradius length to the shortest edge length and the ratio of the tetrahedron volume to its circumscribing sphere volume to control the element quality. For the low-quality tetrahedral element, the mesh is optimized by adding new point. In addition, for the entity with complicated geometry, especially the geologic body containing thin layers, adding constraints can improve the mesh quality and shorten the calculation time. Finally, based on the above algorithm, the program for 3D finite element mesh automatic generation is developed.The effect of earthquake on the formation of landslide is mainly by the wave oscillation of landslide body. The wave oscillation produces two effects in the process of the deformation and failure of the landslide. They are the progressive failure effect and trigger effect. The two failure effects are magnified many times when the main frequency of earthquake load is close to the intrinsic frequency of rock-soil mass. So, when the seismic wave propagates in the rock-soil mass, especially close the surface, the spectrum characteristic of rock-soil mass is the direct factor of affecting the earthquake destructive effect on the rock-soil mass. During earthquake, the landslide often selectively magnifies the seismic wave in some frequency domain, and the intensive oscillation has arisen and induces the occurrence of disaster. It is a typical resonance phenomenon.The modal analysis theory is introduced into the evaluation of seismic landslide. Based on the basic dynamic finite element equations, the 3D theory framework of seismic landslide spectrum analysis is established, and the calculation method of the landslide intrinsic frequency and vibration mode is proposed. Combining with the pre-processing program module of finite element method, the program ASLS is developed. The concept and its calculation method of the dynamic safety factor for seismic landslide are proposed. With reference to the seismic response spectrum characteristic period of seismic parameter zoning map of China, the characteristic frequency of the area can be obtained. The ratio value of the characteristic frequency to the calculated intrinsic frequency of landslide is obtained, ant it is defined as dynamic safety factor. With reference to the method to define the safety factor under seismic load in Specifications of Earthquake Resistant Design for Highway Engineering and Technical Code for Building Slope Engineering, the dynamic safety of landslide under the earthquake in the engineering seismic fortification criterion of China is evaluated by the approaching degree between the dynamic safety factor and '1'. For the unsafe landslide, its failure can be prevented by taking some reinforcement measures to change its intrinsic frequency.The shaking table model test of seismic landslide is designed and carried out. The plain concrete is used to make the landslide models. For each landslide, several vibration tests under different frequency seismic waves are performed. According to the dynamic responses of the landslide model, the frequency range corresponding to the largest displacement of landslide can be found, and it is considered that the intrinsic frequency of landslide is within the frequency range. Finally, the test results and the calculated results of ASLS are comparatively analyzed.By using the self-developed program, the intrinsic and vibration mode of a constant-section cantilever beam fixed by two ends are calculated, the safety of a homogeneous slope is evaluated, and the safety evaluation of a certain landslide in the reservoir area of Three Gorges Project is performed.