ENGINEERING GEOLOGICAL STUDY ON DAGUANGBAO LANDSLIDE

Daguangbao landslide with an area of 7.12km2 and a volume of 1.159 billion m3 is the largest landslide triggered by the Wenchuan MS8.0 Earthquake occurred on May 12th,2008,and also is the largest one in China and one of the few giant landslides more than one billion m3 in the world. It is located in the hanging wall of the seismogenic fault of the Wenchuan earthquake,and 3.0～4.5km away from it. The authors' team has conducted a engineering geological survey including mapping,geophysical exploration,pitting and boreholes with a scale of 1:2000 since 2011. According to the data,we finished a series of geological maps including a comprehensive plane map and 25 sections. The spatial shape of the landslide,pre- and post-failure structures,slip surface and its characteristics were further investigated and a set of quantitative data about Daguangbao landslide features was obtained. We found it was a hugewedge failure with a strike slipping sliding along a bedded shear fault. According to the description of witnesses and structures of the accumulation,we rebuilt the experience of the slope failure and sliding process during the strong quaking. Basically,it can be divided into five stages:shattering-tensile cracking,cutting through of the front locking section,suddenly braking and napping motion,detaching sliding on both sides of the accumulation and finally secondary sliding of the scarp cliff. The accumulation can be divided into three area and ten sub-areas. They are the main scarp area,the accumulation area,and the back depression area,which corresponding to three,four and three sub-areas respectively.