Applying discontinous deformation analysis to assess the constrained area of the unstable Chiu-fen-erh-shan landslide slope

Chiu-fen-erh-shan landslide is a remarkable slope failure occurred during the Chi-Chi earthquake in 1999. In November of 2002, abnormal geomorphologic features, including buckling and ground subsidence, were observed on the lower slope of the Chiu-fen-erh-shan landslide. This study attempts to assess the constrained area of a future collapsing on the slope using a dynamic discrete numerical analysis method, discontinuous deformation analysis (DDA). The simulation results show that the depression in front of the toe of the slope provides a space for arresting the whole sliding rocks when only the unstable lower slope fails. However, as the whole slope slides, the rock fragments move farther into the memorial park and can impact other facilities resulting in the enlarging of constrained area. The authority should prohibit people from entrancing the constrained area in the rainy season.