Drained shear strength parameters of saprock from a weathering profile over porphyritic biotite granite at Km 31 of the Kuala Lumpur - Karak Highway, Peninsular Malaysia

Raj, John Kuna (2022) Drained shear strength parameters of saprock from a weathering profile over porphyritic biotite granite at Km 31 of the Kuala Lumpur - Karak Highway, Peninsular Malaysia. Bulletin of the Geological Society of Malaysia (74). pp. 43-53. ISSN 2637-109X

Abstract

Three broad zones can be differentiated at the weathering profile; an upper, 9.4 m thick, pedological soil (zone I), an intermediate, 31.7 m thick, saprock (zone II) and the bottom bedrock (zone III). The saprock (zone II) comprises gravelly silty sands that distinctly preserve the minerals, textures and structures of the original bedrock and can be separated into sub-zones II A, II B, II C and II D based on differences in preservation of relict structures and content of litho-relicts (core-boulders). To characterize the drained strength of saprock, samples were collected from sub-zones II B, II C and II D, and their physical and soil index properties determined before consolidated, drained triaxial tests were carried out on remolded specimens. Three individual specimens from each sub-zone were consolidated for 24 hours and compressed at a rate of 0.152 mm/min under confining pressures of 138 kPa, 207 kPa and 276 kPa. The tests yielded effective cohesions (c’) of 30.6 kPa, 9.5 kPa, and 20.2 kPa, and friction angles of 33.2°, 31.4° and 34.4°, for the samples from sub-zones II B, II C and II D, respectively. Regression analyses show effective cohesions (c’) to increase with increasing moisture contents retained at 4.19 pF (1,500 kPa) suction; a feature indicating the influence of negative pore water pressures (matric suction). Regression analyses also show effective friction angles to increase with increasing sand, and sand and gravel, contents; a feature indicating increased inter-locking and resistance to displacement of coarse particles during shear. It is concluded that the saprock is characterized by an average effective cohesion of 14.5 kPa, and friction angle of 34.3°; these parameters influenced by the moisture content retained at 1,500 kPa suction, and the sand and gravel contents.

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