Effectiveness of Surface drainage in enhancing the stability of cut slopes during the periods of heavy rain

Abstract

Rain induced failures in slopes made of residual soils are a major geotechnical hazards in Sri Lanka. These soils are characterized by the heterogeneous nature inherited from the variability in the parent rock and the process of variable weathering. Safety margins of these slopes are high during the periods of dry weather due to the prevailing matric suctions. Rainwater infiltration causes a loss of matric suction and builds up of positive pore water pressures.

With the use of sealed drains in the berms, cascade drains to allow rapid passage of water down the slope and appropriate vegetation cover over the slope surface, the infiltration of rainwater can be reduced. The effect of rainwater infiltration on the pore pressure regime and the effectiveness of the said surface drainage measures were studied using the software SEEPW [4]. The stability of the slopes after a rainfall event was analyzed using the software SLOPEW [3]. The complex nature of the residual soil was idealized with zones of different levels of weathering. The results illustrated that the destabilizing effects of rainfall could be minimized with the usage of appropriate surface drainage measures.