Effects of Geological and Geotechnical Characteristics on Cut-Slope Stability of Residual Formations in the Hilly Terrain of Sri Lanka A Case Study from Central Expressway (Section 3)

Abstract

Residual formations consist of residual soils and parent rocks of different levels of weathering due to physical, chemical and biological processes. Existence of residual soils on the hilly slope surface and weathering of parent rocks of the residual formations can cause slope instability problems. Cutting on the hilly slopes during development projects have aggravated the problems. Sri Lankan residual soil formations are formed by weathering of the metamorphic rock and have inherited significant abrupt variations in engineering characteristics. Basic characteristics of these residual formations such as unsaturated shear strength (geotechnical) and variation of geological features (geological) are essential parameters in slope stability analyses. Therefore, a study for effects of geological and geotechnical characteristics on cut slope stability of residual formation was done by selecting major cutting sections on hilly terrain in Central Expressway Project (CEP 03) trace where degree of weathering of the parent rock units, their petrography, physical, mechanical properties and various structural features as well as series of index properties, engineering properties and strength tests on residual soils were performed.This paper highlights the need for detailed experimental studies and presents preliminary studies that have been conducted to establish the geological and geotechnical characteristics of unsaturated Sri Lankan residual formation. The results indicate that the variation in geotechnical as well as geological characteristics of the residual formation are related to cut slope stability in hilly terrain.