Abstract: The Daguangbao (DGB) landslide was the largest landslide triggered by the 2008 Wenchuan earthquake. Its shear-slip failure occurred in the pre-structural interlayer dislocation zone of the slope, which is mainly composed of mylonitized and brecciated tectonic fragments, and has obvious characteristics of groundwater occurrence and movement. In order to study the dynamic behavior of the dislocation zone and its possible influence on the start-up of Daguangbao landslide under the participation of groundwater during strong earthquakes, a series of triaxial tests including hydrostatic triaxial, unidirectional and bi-directional dynamic triaxial tests was conducted in the laboratory on the materials sampled from dislocation zone to analyze the liquefaction characteristics of the materials. The experimental results show that the material has strong potential liquefaction capacity; under unidirectional and bi-directional dynamic loads, the material can liquefy, but the liquefaction rate of bi-directional vibration is faster, and the dynamic strength decreases by about 20% than that of unidirectional vibration. Under bi-directional vibration, the liquefaction rate of material increases with the increase of cyclic deviating stress and radial cyclic stress, and the liquefaction rate under the phase difference 180ois faster than that under the phase difference 0o. The dynamic condition of bi-directional triaxial test may be closer to the actual stress state for the interlaminar staggered zone of Daguangbao landslide with inclined occurrence (N2oW/NE/30o); liquefaction of the staggered zone may be the cause of the sudden start of Daguangbao landslide during the strong earthquake.

Key words: DGB landslide, cyclic triaxial test, liquefaction within the sliding zone, landslide start-up, interlayer dislocation zone