Mineralogical Evolution and Geo-mechanical Characterization of Weathering Profiles Along the Central Expressway (CEP 3), Sri Lanka

Abstract

This research investigates the mineralogical and geo-mechanical factors influencing slope stability along Section 3 of the Central Expressway Project (CEP 3), Sri Lanka. Through a combination of borehole logging, petrographic analysis, and X-ray diffraction (XRD), a comprehensive weathering profile was established. Results delineate a transition from stable, fresh metamorphic gneissic rocks to highly unstable residual soils (SM and ML types). Petrographic data reveal the progressive alteration of primary minerals, specifically Feldspar, Biotite, and Hornblende, into secondary Clay phases. XRD analysis identified the presence of Smectite and Kaolinite, with the former presenting significant risks for moisture-induced volume changes and rotational slides in high-cut sections. The study concludes that the thickness and stability of the residual mantle are directly governed by the modal mineralogy of the metamorphic parent rock, providing a critical framework for geotechnical risk mitigation in hilly terrains