Abstract: The ancient landslide is of ancient origin, complex in cause, and difficult to locate. However, when engineering activities pass through, due to the impact of the human disturbance, ancient landslides are very prone to reactivation, posing a serious threat potential to the engineering projects. The Taozhou ancient landslide is presented in this paper as an example. The combination of the drilling and the geophysical exploration methods was used to conduct engineering geological investigations of the ancient landslide site, obtaining the engineering geological conditions of the area. The landslide site is a medium-thick layer large landslide body formed by accumulation and traction. Based on the nature and the characteristics of the landslide deformation, combined with survey data, key factors affecting the stability of the ancient landslide were identified: the material composition and the structural characteristics; topographic conditions; the continuous rainfall and the groundwater; and the human engineering activities. The limit equilibrium method was used to evaluate the stability of the ancient landslide. The analytical results indicate that the ancient landslide site is overall in a marginally stable state; however, since the landslide body is mainly loose accumulation, the results of local stability analysis show that the small-scale accumulation landslides will occur at the front of the ancient landslide. This analysis result is consistent with the on-site investigation, where two small collapses were observed at the front of the landslide. Finally, a comprehensive analysis of the above results provides some suggestions for the highway alignment and the treatment of the collapsed body at the front of the landslide.

Key words: Ancient Landslide Site, Reflection Wave, Limit Equilibrium, Transfer Coefficient Method, Local Instability