FAILURE MECHANISM ANALYSIS CONSIDERS THE HYDROLOGICAL AND SEISMIC CONDITIONS AT CHASHAN SITE IN CENTRAL TAIWAN

Abstract. The investigation results of large-scale landslides in the central part of Taiwan from Central Geologic Survey identified a new, largescale landslide in the Chashan Village of Alishan Township, Chiayi County (ID: D160) which has the potential to influence the safety of Chashan Village residents. In coordination with the surface geological survey, Chashan site can be divided into three potential sliding areas (zones A, B and C). The paper uses GeoStudio for evaluating the stability of different hydrological and seismic scenarios. The results of scenario simulation show that: (1) In the normal and high water level scenarios, the safety factor obtained in zone A is greater than 1.0, and the initial judgment belongs to the stable state; (2) In the earthquake scenarios, the A4 potential sliding mass in zone A will be collapsed; (3) Through the scenario simulation, when the water level in zone A rises more than 25 meters or the PGA exceeds 160 gal, it is possible to cause the collapse of A4 potential sliding mass. The result of the study will contribute that the complex phenomenon between the stability of landslides and hydrogeological conditions can be revealed and clarified through the detailed study on the hydrogeological investigation, observation and the numerical simulation.