Investigation of suitable methods to protect main roads adjacent to water bodies

Abstract

Main roads adjacent to water bodies often face significant stability challenges due to erosion caused by, heavy rainfall, increased water flow along riverbanks, the sudden drawdown of water levels after flooding, sand mining and various other human activities within river catchments. These conditions can lead to failures in the river banks disrupting the functioning of the road. This thesis presents four such problematic locations, identifying the root cause of the problem and presenting appropriate different rectification measures adopted. Common features and different aspects at the four locations are elaborated. The locations all in the Western Province are; Kelani River bank along the low-level road, the right side of the Halwathura Phalakotasa stream bank along the Ingiriya-Halwathura-Ekgaloya road, Halkotiyawatta stream bank on Seelarathana Mawatha, and Diyawanna Lake bank on Denzil Kobbekaduwa Mawatha. A comprehensive literature review was done on various techniques involving both hard and flexible solutions, including reinforcing techniques and integrating natural vegetation developed in different parts of the world over the last decade. Novel approaches appropriate for Sri Lanka were proposed based on the findings of the literature review. At each location, different alternatives were closely evaluated considering cost, constructability and sustainability to decide on the best to be adopted. Stabilization techniques evaluated are; (1) Gabion wall with rock packing at the toe, (2) vegetated live bamboo crib wall construction with Gabion at the toe, and (3) vegetated flapped soil bag with live stake retaining structure with a Gabion at the toe. The proposals were implemented at three locations and the performance is being monitored. The satisfactory performance over few years serves as an encouragement to adopt sustainable techniques in infrastructure development in Sri Lanka.