The Alishan Forest Railway has frequently suffered landslides, landslips and debris flows caused by different natural hazards. During Typhoon MORAKOT, several large landslides occurred. In this study, two severely damaged sections were selected as the pilot areas. Geological
investigations were conducted to investigate the failure mechanisms. The first selected area is in Erwanping. This area has an old landslide area with a dip slope. The failure mechanisms of this collapsed area include a deep landslide with colluvium material and erosion. The second selected area is the collapsed area in the Duolin area. The rock joints in the slope formed rock wedges which fell down easily. The failure mechanisms of this collapsed area include decomposition of rock stratum, a deep landslide and erosion. After a comprehensive discussion, tunneling transportation is chosen because it is a better way to pass through the collapsed areas and the maintenance of a tunnel is much easier in these collapsed areas.
Key Words : Alishan forest railway, MORAKOT typhoon, large-scale landslides, geological investigation,complex destruction.