The Tsaoling landslide triggered by the Chi-Chi earthquake, Taiwan: Insights from a discrete element simulation

In the village of Tsaoling (in Yunlin County, Taiwan), a major landslide was triggered by the Chi-Chi earthquake in 1999 with more than 125 × 106 m3 of rock displaced. The kinematic behaviour of this landslide is simulated using a 2D discrete element model (PFC2D code). Our numerical model is composed of discs bonded together. The initial boundary conditions are applied along the ball-wall contacts by using derived velocities integrated from the strong motion data with a duration of 160 s including the peak acceleration near Tsaoling. The constraints are mainly issued from the final geometry of the landslide including its capacity to cross the river valley and reach a significant elevation on the opposite mountain flank. They also result from a variety of geological and hydrological observations, including the local levels of material disruption and the location of survivors. Our modelling thus indicates that a low-friction coefficient (about 0.15) and a medium strength are required to account for the actual landslide characteristics. A self-lubrication mechanism probably accounts for the low residual friction. Our model also suggests that the maximum velocity of sliding reached 50 m/s, a result that cannot be checked in the absence of actual measurements. In addition to friction, the strength of sliding block is of special importance because it controlled the possibility for the upper layer fragments to roll and get buried, and hence the probability of survival.