The Development Characteristics And Genetic Mechanism Of Slope Failure In The Wenchuan Earthquake Epicentral Area

Collapse is one of the most important geological disasters in the mountain, Wenchuan earthquake induced extensive collapse disasters and exacerbated the damage and losses in the earthquake zone. Aftershocks happened frequently, make some shattered slope destroyed again. Therefore, there have important theoretical and practical significance for the research of epicentral collapses’ development characteristics and genetic mechanism.In this paper, we choose the collapse hazard in the epicentral area of the Yingxiu and its nearby areas as the research object.Based on the detailed site investigation,development and factors of the geological disasters on slope are analyzed by the method of statistics and simulation.And then a further study on law of slope dynamic response in conditions of seismic loading and the topography is shown while the Zaojiaotuo collapse is simulated to declear the dynamic response law as a examle.Research results are as follows:(1)Medium-scaled and large-scaled collapse accounted for 90% geological disaster after earthquake.Collapse on the right bank either in intensive degree or in scale is greater than that on the left. At the same time the distribution also has obvious effect on the plate and back slope effect.(2)The development of collapse focused on thin ridge site, isolated hills and prominent spur site which facing an empty in three directions within the study area. Slope shape and slope height also have a significant effect on the development of collapse, which mainly developed in the slope height of 200 ~ 600 m, the slope of 45 ~ 69 °, slope aspect in the 61 ~ 150 °, and is mainly developed in the 3H / 4 ~ H of slope height position. The upper part of concave and convex slopes are more prone to collapse. The slope break site of polyline slope are more prone to collapse. Collapses develop scarcely on rectilinear slope.(3)Under the action of seismic wave with different period, the horizontal displacement increases with the increase of seismic period,when the seismic period exceeds a certain value, the displacement of extreme value will be decreased with the increase of seismic period. Seismic period has enormous influence on the stress distribution of slope:When the seismic period within a certain range, with the increase of slope height, the stress distribution showed a trend of gradual increase in value, when beyond this range, the slope stress will decrease with the increase of elevation. Seismic amplitude has little effect on distribution of the slope dynamic response, changes in the amplitude can scarcely change the slope displacement and stress distributions, but the extreme value is gradually increasing with the increase of seismic wave amplitude.(4)Under different slope shape, the horizontal displacement values from the slope to the top is roughly showing a trend of increase from the toe to the top, extreme maximum value of horizontal displacement belong to concave slope, followed by rectilinear slope, the smallest for convex slope; The stress nephogram of different slope shape are basically the same, stress value have a linear increasing trend from toe to the top, stress contour strip substantially parallel to the top of the hill, extreme maximum value of stress belong to concave slope, followed by rectilinear slope, the smallest for convex slope. With the increase of slope height, horizontal displacement value and the stress value will show a increase, decrease, and then increase the of the circulation change process, and there has a minimum stress stripe of stress throughout internal slope. When the slope height is constant,the changing gradient of slope has some impact on the level of horizontal displacement and stress distribution, but both extreme values don’t increase with the increasing slope gradient, which has no obvious linear relationship.(5)Slope topography amplification effect in the magistoseismic area performs significantly.Zaojiaotuo collapse don’t destroy instantaneously or balanced unstable failure, due to the influence of the terrain amplification effect, the top first form stress concentration, along with the continuous seismic dynamic input, stress concentrated to the front of the locked segment of slop,slope vibrate with cracking, rupture, the upper rock mass collapse and sliding, then apply thrust power to the lower part of the rock mass, which finally leads to the whole body collapsing. Analysis revealed that particle acceleration in the slope body has terrain amplification effects under the action of seismic force and the most obvious level of seismic wave belongs to acceleration amplification effect, vertical acceleration, followed by level to the speed, vertical velocity amplification coefficient is minimal. Comparing the speed amplification factor of monitoring points between structural surface and bedrock, which proved that slide starts with a greater acceleration, the results also prove that, in the process of seismic wave propagation, the high and steep terrain with a parallel slope controlled by steep structure plane have a significant amplified effect on seismic wave. Amplify peak acceleration —The Increasing amplitude force rock mass along the controlling structure planes which parallel with slope to crack quickly —Slip along the gently dipping levels—High-speed detach from the slipping source region —Huge potential and kinetic energy drive rock mass to do long-distance movement, which is the movement mode of this slop.( 6) Unlike rain induced collapse, special part in slope vertical peak acceleration and level peak acceleration amplified by topography at special part of slope, the surface structure of rock lose the connect power under the action of tensile stress and slop finally destroy under the coupling effect of inertia force and gravity. Slope failure mode is given priority to the slipping and dumping form with the characteristics of mass ejection in the magistoseismic area.