Impact of weathering on geotechnical properties of metamorphic rocks on part of the Kurunegala - Kandy expressway

Weathering is an irreversible naturally occurring phenomenon that negatively affects the structural integrity and geotechnical parameters of rocks. This study aims to understand how weathering influences the physical parameters of tropical metamorphic rocks, by testing three types of gneissic rocks — Granitic Gneiss, Quartzo-Feldspathic Gneiss and Biotite Gneiss — collected along the Pothuhera – Galagedara Section of the Central Expressway, Sri Lanka. Rocks were tested under three main degrees of weathering for each rock type, using UCS, Brazilian tensile strength, slake durability, AIV, and LAAV. Results show that Biotite Gneiss deteriorates the fastest under weathering and is the most vulnerable to wear. Consequently, although Granitic Gneiss has the highest strength initially, it declines rapidly. Comparatively, Quartzo-Feldspathic Gneiss has lower initial strength than the other two rock types, but retains it more effectively as weathering progresses.