CHARACTERISTICS OF FORMATION MECHANISM AND KINEMATICS OF DAGUANGBAO LANDSLIDE CAUSED BY WENCHUAN EARTHQUAKE, SICHUAN, CHINA

The Wenchuan M 8.0 earthquake on May 12, 2008 caused thousands of rock falls and landslides. The Daguangbao landslide in Anxian County is the largest landslide site. Its failed slope volume is up to 1billion m3.Its formation mechanism and kinematics attract a wide attention of scholars at domestic and abroad. Based on a series survey of the landslide field measurement and laboratory experiments, this paper presents some new understandings of the landslide as follows.(1)the landslide is a wedge and trough shaped fall. The bottom Sinianperiod dolomitite layer functioned as the main surface of rupture. The early X-tectonic fractures that orthogonal to the layer functioned as a side surface of rupture. The intersection line of two control planes tends to 64with dip angle 12.(2)the Huangdongzi valley in front of landslide is the outlet of the surface rupture. The landslide rapidly slipped into the valley. The moving mass was obstructed and braked by the valley slope on its left side. The upper part of landslide mass passed over the left valley slope and developed a debris flow.(3)the rupture plan of the landslide is along a layer of Sinian dolomite rock mass. It experienced strong karstification and became a band layer of sand-soil. This sand-soil layer during the strong vibration changed its performance caused by the suddenly increase of excess pore pressure. Even then, it developed into a fluidal structure layer. This may be the main formation mechanism of this huge landslide. Daguangbao landslide may be the new model of mountain collapse that caused by earthquake. The research on the analysis of the evolution and the stability of the slope has an important meaning.