Economizing Soil Nailing Design by Drainage Improvement—Case History at Ginigathhena

As a tropical country which faces two monsoons with heavy precipitation, rainfall is identified as the major triggering factor for landslides in Sri Lanka. Reactivation of ancient landslides is a major challenge faced by the engineers in infrastructure development in the hilly terrain of the country. An ancient landslide at Bridge No. 48/2 in Avissawella—Hatton—Nuwaraeliya road was reactivated by excavation at the toe for the proposed widening of the bridge. This propagated further by the extensive rainfall that occurred subsequently. The site is a sloping ground with undulating topography towards upper slope in the form of a valley formed by an ancient landslide. Mitigation of the landslide was done to accommodate the widening of the bridge and to minimize the risk of further activation by rainfall. Mitigation measures adopted were drainage improvement, slope modification and soil reinforcement. Soil nailing was used as the reinforcement technique. Surface and subsurface drainage improvement was used for economizing the nailing design. This study presents how the nailing design was optimized by using different drainage arrangements. GeoStudio SEEP/W and SLOPE/W software were used for seepage and slope stability analyses, respectively.