The Analysis Of Seismic Dynamic Response Of Slopes In Mountains With Complex Geological Backgrounds

Earthquake is a major triggering factor of slope instability; it will cause collapses, landslides and debris flows. China is a country with a lot of mountains and a high frequency of earthquakes. Thousands of geo-hazards which included landslides and collapse were triggered by the May 12th Wenchuan Earthquake ,and casued a great damages and losses. The study on the law of the seismic dynamic response of slopes turned out to be an important theory and with a practical significance.This paper is based on the characteristics of the seismic dynamic response of slopes on the May 12th Wenchuan Earthquake. Through a detailed field investigation on the failure and damages of slopes during Wenchuan Earthquake, by means of numerical simulation and physical simulation which were applied to do a systematic study on the impact law of the influences of the seismic force on the slope deformation and failure , the study targets include the topography of slopes, materials of slopes and the conditions of dynamic loads, then analyzed the mechanism of the seismic forces on the slope , and discussed the major patterns and processes of slope instability which triggered by earthquake. The study summarized the following laws of the seismic dynamic response of slopes.1) The dynamic response of slopes with non-linear changes. Dynamic responses are changing both in the horizontal direction and vertical direction. In gerneral, the dynamic response of seismic waves is more strongly on the upper parts of the slope and on the surface of the slope.2) The vertical seismic force attributes less to the slope deformation and failure than the horizontal seismic force. The amplitude of seismic dynamic load has little effect on the distribution law of the dynamic response of slope. The distribution form of acceleration amplification coefficient is basically the same under different amplitude of Seismic loads. The frequency of dynamic load has an obvious effect on the dynamic response of slopes. Under the common conditions, it can be concluded that the higher the frequency of dynamic load, the greater the difference in response to acceleration.3) There's not a linearly increase of the amplification of the Seismic acceleration with the increasing of the angle or height of slope. In the slopes with 20 ~ 50°slope angles, the seismic response of slopes is very obviously. The higher of the slope, there will be more maximum area of the acceleration and velocity amplification coefficient, and there will be more changes of the increase and decrease. Terrain on the slope has apparent effect on the dynamic response of slopes. Seismic wave has a significant amplification effect in the changing parts of the terrain, such as the turning parts of the terrain, thin parts of the ridge, isolated hill or the mountains of multi-face empty part.4) The dynamic response of the slopes in hard rock is greater than the dynamic response of the slopes in soft rock. The slopes of hard rock usually occurs collapse, and the slopes of soft rock and soil usually occurs landslide.5) The horizontal seismic inertia force brought vertical tensional cracks which strike perpendicular to the direction of the seismic force on the top of the slope firstly. At the same time, it drive the plasmodium on the out side of the crack move along the horizontal direction, brought the tensional and shearing texture surfaces which have the tendency the same as the direction of the moving. At last, the slope failed along this surface. The process of seismic force affect on slopes can be generalized into four stages which include the emergence of cracks, the deformation to the direction of the invading, the development of cracks and the failure of the slopes.