Abstract
It is known that rainwater infiltration is crucial for rainfall-induced slope failure because the infiltrated water can significantly weaken the shear strength of unsaturated soil. Horizontal drains are commonly used to provide appropriate drainage for the rainwater that percolates out of a slope. However, the effects of the length and location of the subsoil pipe on the performance of horizontal drains have not been extensively investigated. In this paper, a parametric analysis by using a numerical model was adopted to investigate the distribution of pore-water pressure in a slope. The results reveal that an inclination angle of 10–15 degrees and strategic placement at the slope toe and mid-slope provide optimal drainage performance, as compared to the effect of pipe length. Multi-layers of horizontal drain (based on 10 m length) are recommended for slopes with a height of more than 15 m.