FAILURE MECHANISM OF PREFERRED STRUCTURE PLANE CONTROLLED LITHOLOGIC SLOPE DURING INTENSIVE EARTHQUAKE

According to statistics, the damage caused by earthquake-induced landslides and collapses can account for about 40% of all that causes by earthquake. As for the mechanisms and modes of slope deformation and failure under seismic force,a lot of previous theories and achievements have been reached. But, numerical simulation research is limited. The seismic intensity of the northern mountainous area of Shifang City, Sichuan province reached 11 degrees during the 5.12 Wenchuan earthquake. The remote sensing system had interpreted up to 161 sites of geological hazards induced by that. Their basic failure modes are bedding-layer cutting slides and slipping collapses. This paper considered two typical geo-hazards triggered by the 5.12 Wenchuan earthquake, and analyzed their stereographic projection. it worked out the combination modes of preferred structure planes which controlled the slope stability. Then it applied numerical simulation with discrete elements software to simulate their process of failure. The results show the following two failure modes. The first mode of slope failure during earthquake is that, the layered slopes that dip gently outwards crack its top at first, meanwhile the structure planes inside the slope start to undergo shear deformation. As the cracks on the top extend downwards and when these cracks reach the structure planes dip outwards inside the slope, the entire slope will slide along those connected planes. Their deformation and failure mechanism is slide-rip. Their mode of failure is bedding-layer cutting slide. The second mode of slope failure during earthquake is as follows. The steep block slopes crack their tops and loose themselves at first. Then the blocks cut and formed by structure planes start to undergo shear deformation along the structure planes which dip gently inwards or horizontal at the bottom of those tensile cracks. Then these blocks gradually slip outwards due to the durative earthquake, roll and fall down the slopes. Their deformation and failure mechanism is rip-slip. Their mode of failure is slipping collapse.