Effectiveness of siphon drainage method for landslide stabilization in a tropical volcanic hillslope: a case study of Cibitung Landslide, West Java, Indonesia

An effort to implement a siphon drainage system requires a comprehensive knowledge of the factor affecting the performance of the drainage system to reduce the groundwater table in the landslide area. A long-term field experiment was conducted to evaluate the effectiveness of the siphon drainage system with vertical wells to maintain the stability of landslide masses in a volcanic hillslope in West Java. The groundwater levels in all wells and water discharged from each well were monitored and measured periodically. Results of a 1-year measurement of the groundwater level indicate that the siphon drainage system was generally effective in decreasing the groundwater level in the landslide masses to a maximum depth of 7 m with a maximum total drainage flow of 24 m3/day. The implemented siphon drainage system was also able to prevent the groundwater level from rising during a rainfall period. A series of slope stability analyses under a steady-unsteady state seepage condition indicates the siphon drainage increased the long-term stability of the landslide area significantly. Based on this study, factors affecting the effectiveness of long-term siphon drainage performance are thoroughly evaluated.