Slope cuts in granitic bedrock areas expose weathering profiles that can be differentiated into three broad morphological zones. The topmost Zone I comprises stiff to very stiff, gravelly sandy clays with indistinct relict bedrock textures, whilst the middle Zone II consists of medium to very dense, gravelly silty sands showing distinct relict textures and structures, and also containing coreboulders. The bottom Zone III of bedrock only shows effects of weathering along and between structural discontinuity planes. At steep cuts and benches (> 60o) exposing Zone I, small earth falls and shallow slips can occur during rainfall due to saturation and loss of strength with time. At steep benches (> 55o) exposing Zone II with day-lighting relict discontinuity planes, wedge failures can occur due to saturation and low shear strengths. During periods of intense or continuous daily rainfall, slumps, slump-flows and debris flows can occur at moderately to steeply sloping (> 45o) cuts exposing Zones I and II, as a result of rainwater induced saturation and loss of suction within the slope materials. Where steep benches (> 55o) expose Zone III, block slides, slab slides, wedge and toppling failures can occur as a result of favourably oriented discontinuity planes having low shear strengths. Rock falls occur where the bedrock is closely fractured.
Deep weathering profiles are found over granitic bedrock in Peninsular Malaysia as a result of favourable environmental and tectonic conditions that have facilitated intense and pervasive chemical weathering (Raj, 1982). These profiles are found in undulating to hilly and mountainous areas and are well exposed at slope cuts excavated during the construction of transport routes. Prior to these discussions is a generalized description of the earth materials into which the cuts are excavated by reference to a typical weathering profile developed over granitic bedrock.
