Three-dimensional analysis of a deep-seated landslide in central Taiwan

The unstable slope, which is located at Lushan, central Taiwan, slid when heavy rainfall occurred in recent decades, posing a threat to a nearby village. Slope stability analysis in three dimensions is more realistic and can advance comprehension of the sliding mechanism. The landslides caused by two heavy rainfall events are simulated in sequence using finite element modeling. The three-dimensional (3D) modeling is established according to the data of extensive investigations, including field reconnaissance, borehole drilling, laboratory experimentation, and monitoring of groundwater tables and displacements. In particular, it requires skills for the generation of a sliding surface and the division of the 3D model. The difference in lithology and a joint set initiated the instability of the slope, forming the fractures on the slope. The sliding surface with greatest depth over 100 m has not yet extended to the lower slope, resulting in greater displacements on the upper and middle slopes than those on the lower slope. The 3D numerical modeling not only reasonably simulates the displacements induced by the rainfall events, but also enables 3D visualization and details of the sliding mechanism. Also, it is capable of revealing the features that cannot be explained in a 2D analysis.