Bulletin of the Geological Society of Malaysia, Volume 71, May 2021, pp. 1 – 11
John Kuna Raj
No.83, Jln. Burhanuddin Helmi 2, Taman Tun Dr. Ismail, 60000 Kuala Lumpur, Malaysia
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Abstract: Three broad zones can be differentiated within the weathering profile over porphyritic biotite granite at Km 31 of the Kuala Lumpur – Karak Highway. The top Zone I (pedological soil) is 12 m thick and comprises A, B and C soil horizons; the C horizon (saprolite) being a clayey sand with indistinct relict bedrock textures. The intermediate Zone II (saprock) is some 30 m thick and consists of silty sands that indistinctly to distinctly preserve the minerals, textures and structures of the original granite. Zone II can be differentiated into four sub-zones; the upper II A and II B sub-zones marked by an absence of core boulders, whilst the lower II C and II D sub-zones have some to many core-boulders. The bottom Zone III (bedrock), whose upper surface is marked by an unconfined groundwater table, is a continuous granite outcrop with effects of weathering along and between discontinuity planes. Constant head permeability tests show saturated hydraulic conductivity (Ks) to vary with depth and texture; clayey sand from saprolite having a conductivity of 0.2420 cm/hr and silty sand from sub-zone II B, a conductivity of 0.7464 cm/hr. Silty sands from sub-zone II D have saturated hydraulic conductivity values of 1.5313, and 1.9585, cm/hr, whilst a silty sand from sub-zone II C has a conductivity of 4.1131 cm/hr due to it being collected at a relict pegmatite pod. Regression analyses show variable trends with low to moderate correlation coefficients (R2 <0.600) for hydraulic conductivity versus index properties as clay and sand contents, but large correlation coefficients (R2 >0.820) for hydraulic conductivity versus physical properties as dry unit weight and void ratio.
Keywords: Weathering profile, porphyritic biotite granite, saturated hydraulic conductivity