STUDY ON THE FORMATION MECHANISM OF TANGJIASHAN LANDSLIDE TRIGGERED BY WENCHUAN EARTHQUAKE USING DDA SIMULATION

Abstract

Wenchuan earthquake, Ms 8.0 in magnitude and occurred on May 12, 2008 in Sichuan Province, China, triggered a lot of landslides, rock collapses, debris flow, etc. The Tangjiashan landslide, with its total volume 20.37 million m3, was the biggest and the most notable one for its effects. Based on the field geological investigation and the typical acceleration records of the main shock obtained in the period of the earthquake, numerical simulation of the whole sliding process of Tangjiashan landslide has been carried out by DDA method. It is shown that the Tangjiashan landslide was a high-speed landslide, behaved with nonlinear features in the whole sliding process. The total duration of the landslide was about 30 s while nearly all of their slipping displacements were carried out in the beginning 25 s, with the maximum sliding velocity about 30 m/s, and the average 15–17 m/s in the beginning 25 s. The crash of rock blocks induced a much higher stresses near the middle and lower parts of the landslide, with the maximum value of 6–7 MPa. The dynamic earthquake load caused an incessant deformation of the landslide, resulting in the reduction of mechanical parameters, especially the shear strength on the sliding surface and the ratio of friction coefficient on sliding surface in kinematical and static conditions are no more than 0.35. DDA simulation considering the displacement-based parameter reduction has been developed in the original DDA code, and its results primarily reflect the evolvement process of a landslide under strong seismic loads.