Three-Dimensional Numerical Investigation on the Efficiency of Subsurface Drainage for Large-Scale Landslides

This paper presents a field monitoring study with emphasis on the design and construction of a subsurface drainage system and evaluation of its stabilization efficiency on the slope of You-Ye-Lin landslide using a three-dimensional finite element method program (Plaxis 3D) for the groundwater flow and slope stability analyses. The subsurface drainage system consists of two 4-m diameter drainage wells with multi-level horizontal drains and was installed to draw down the groundwater level and stabilize the unstable slope of the landslide. Results demonstrate that the subsurface drainage system is functional and capable of accelerating the drainage of the infiltrated rainwater during torrential rainfalls during the typhoon season. The large groundwater drawdown by the subsurface drainage system protects the slopes from further deterioration and maintains the slope stability at an acceptable and satisfactory level.