A Case Study of Slope Instability Caused by Weathering Process of Phyllite, Meta-Arenite and Granite on the Pergau and Kenyir Slopes

Abstract

Due to the disturbed rock mass and topographic conditions caused by earthworks, slopes are highly susceptible to weathering. During and just after the earthworks of a slope, the exposed rock material and mass may be subject to weathering and erosion. They may erode and alter the rock's engineering properties and the stability of the slope over the rock's engineering lifetime. This study examined the effects of weathering on the stability of two cut slopes in Phyllite, Meta-Arenite, and Granite from Pergau, Kelantan, and Kenyir, Terengganu. This study used a spatially integrated mapping framework to examine slope instability in remote tropical forests and natural hilly terrain using spatial data analysis that contributes to the development of landslide hazard map, slope aspect, slope angle, slope orientation, and shaded slopes (i.e., slopes of some orientations are more sheltered (shaded)) from sunlight than slopes of other orientations and elevation. This framework identified and validated slope instability utilizing a confirmatory site-specific analysis and laboratory tests, including uniaxial compressive strength and geophysics survey to examine weathering grade and groundwater level, including the saturated condition of the rocks. Field data show that the weathering occurs due to percolating groundwater and due to the slope, which is protected from the direct rays of the sun and can retain more moisture, causing a gradual degradation of the rock's engineering properties of the slope. Based on what has been seen in the field and the analysis, the safety factor for mass failure on the study slopes is usually the key determinant. Based on limit equilibrium analyses, both cut slopes likely fall apart in a plane with a low safety factor.