Warta Geologi, Vol. 50, No. 3, December 2024, pp. 184–191
John Kuna Raj
Geology Consultant, 83, Jalan Burhanuddin Helmi 2, Taman Tun Dr. Ismail, 60000 Kuala Lumpur
Email address: jkr.ttdi.tmc@gmail.com
Abstract: Slope cuts in weathered graphitic-quartz-muscovite schist expose an upper pedological soil (3-4 m thick) of silty to sandy clays with lateritic concretions, and a lower saprock (>10 m thick) of alternating bands of variously colored, firm to stiff and hard, clayey silts and silts with indistinct to distinct relict bedrock minerals, textures and structures. Moderately sloping (<60°), low cuts (<15 m high) in unsaturated, weathered schist are unaffected by failures, though small slips and falls have sometimes occurred at steeper cuts during rainfall events. To validate the role of negative pore water pressures in influencing the stability of slope cuts, laboratory pressure plate tests were carried out on weathered graphitic-quartz-muscovite schist collected at depths of 5.83 m (A), 6.71 m (B) and 8.95 m (C) at a weathering profile in the Kajang Schist. Samples A, B, and C, with dry unit weights of 12.76, 14.73, and 13.23, kN/m3, and porosities of 51%, 44%, and 49%, are overwhelmingly fine gained with silt contents of 53.6%, 73.7%, and 76.6%, and clay contents of 35.0%, 14.0%, and 23.0%, respectively. Increasing suctions from 0 kPa through 0.98 kPa and 9.8 kPa to 33 kPa and 1500 kPa resulted in volumetric moisture retentions of 49.9% through 48.9% and 36.7% to 33.0% and 7.2% in sample A, from 51.8% through 48.6% and 41.1% to 34.3% and 4.5% in sample B, and from 55.5% through 53.2% and 47.6% to 30.2% and 8.6% in sample C. Best fit lines drawn with the van Genuchten (1980) parametric model indicate rapidly decreasing moisture contents with increasing suction due to large porosities. It is concluded that negative pore water pressures in unsaturated, weathered graphitic-quartz-muscovite schist give rise to an enhanced shear strength and stability of slope cuts, though rapid infiltration of rainwater results in saturation and failure.
Keywords: Weathered graphitic-quartz-muscovite schist, moisture retention, suction, negative pore water pressures, slope cut stability
References
Agus, S.S., Leong, E.C. & Rahardjo, H., 2001. Soil-water characteristic curves of Singapore residual soils. Geotechnical & Geological Engineering, 19, 285-309.
ASTM, American Society for Testing Materials, 1970. Special Procedures for Testing Soil and Rock for Engineering Purposes. Special Publication 479, American Society for Testing Materials, Philadelphia. 630 p.
Brooks, R.H. & Corey, A.T., 1964. Hydraulic Properties of Porous Media. Hydrology Paper, 3, Colorado State University, Fort Collins. 37 p.
Bujang, B.K.H., Faisal Hj. Ali, & Hashim, S., 2005. Modified shear box test apparatus for measuring shear strength of unsaturated residual soil. American Journal of Applied Sciences, 2(9), 1283-1289.
Easton, Z.M & Bock, E., 2016. Soil and soil water relationships. Virginia Cooperative Extension, Virginia Tech, Virginia State University, Publication BSE-194P. 9 p. https://ext.vt.edu>a griculture>water>department. Downloaded 17 Dec 2020.
Fredlund, D.G. & Morgenstern, N.R., 1977. Stress state variables for unsaturated soils. Journal Geotechnical Engineering, 103, 447–466.
Fredlund, D.G. & Xing, A., 1994. Equation for the Soil-Water Characteristic Curve. Canadian Geotechnical Journal, 31(4), 521-532.
Hamdan, J., Burnham, C.P. & Ruhana, B., 1998. Physico-chemical characteristics of exposed saprolites and their suitability for oil palm cultivation. Pertanika Journal Tropical Agricultural Science, 21(2), 99-111.
Hamdan, J., Ching, L.B. & Ruhana, B., 2006. Saturated hydraulic conductivity of some saprolites from Peninsular Malaysia. Malaysian Journal of Soil Science, 10, 13-24.
JKR, Jabatan Kerja Raya, Public Works Department of Malaysia, 2007. Guidelines for Hard Material/Rock Excavation. Technical Note (Roads) 24/05. Road Division, Jabatan Kerja Raya Malaysia, Kuala Lumpur. 15 p.
Lee, C.P., 2009. Palaeozoic Stratigraphy. In: Hutchison, C.S. & Tan, D.N.K. (Eds.), Geology of Peninsular Malaysia, University of Malaya and Geological Society of Malaysia, Kuala Lumpur. 479 p.
Noguchi, S., Baharuddin, K., Zulkifli, Y., Tsuboyama, Y. & Tani. M., 2003. Depth and physical properties of soil in a forest and a rubber plantation in Peninsular Malaysia. Journal of Tropical Forest Science, 15(4), 513-530.
Rahardjo, H., Satyanaga, A., Leong, E.C., & Ng, Y.S., 2010. Effects of groundwater table position and soil properties on stability of slopes during rainfall. Journal of Geotechnical & Geoenvironmental Engineering, 136(11), 1555-1560.
Rahardjo, H., Kim, Y., & Satyanaga, A., 2019. Role of unsaturated soil mechanics in geotechnical engineering. Journal of Geo- Engineering, 10, 8. https://doi.org/10.1186/s40703-019-0104-8.
Raj, J.K., 1983. A study of residual soils and their cut slope stability in selected areas of Peninsular Malaysia. Ph.D. Thesis, Faculty of Science, University of Malaya. 462 p.
Raj, J.K., 1995. Clay minerals in the weathering profile of a graphitic-quartz-muscovite schist in the Kajang area, Selangor. Warta Geologi, 21(1), 1-8.
Raj, J.K., 2001. Failures of slope cuts in weathered schists of the Kajang Area, Peninsular Malaysia. Proceedings Forum Geology & Geotechnics of Slopes, Geological Society of Malaysia & Institute of Engineers Malaysia, 23 October 2001, Petaling Jaya, 1-15.
Raj, J.K., 2009. Geomorphology. In: Hutchison, C.S. & Tan, D.N.K. (Eds.), Geology of Peninsular Malaysia, University of Malaya and Geological Society of Malaysia, Kuala Lumpur. 479 p.
Raj, J.K., 2010. Soil moisture retention characteristics of earth materials in the weathering profile over a porphyritic biotite granite in Peninsular Malaysia. American Journal of Geosciences, 1(1), 12-20.
Raj, J.K., 2021. Soil moisture retention characteristics of saprock from the weathering profile over a biotite-muscovite granite in Peninsular Malaysia. Warta Geologi, 47(3), 217-225.
Raj, J.K., 2023. Soil moisture retention characteristics of saprock in a weathering profile over rhyolite in Peninsular Malaysia. Warta Geologi, 49(2), 53-63.
Scherer, T.F., B. Seelig & Franzen, D., 1996. Soil, water and plant characteristics important to irrigation. EB-66, www. ag.ndsu.edu/pubs/ageng/ irrigate/eb66w.htm.
USBR, United States Bureau of Reclamation, 1974. Earth Manual. United States Government Printing Office, Washington. 810 p.
van Genuchten, M.Th., 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal, 44, 892-898.
Weiler, M. & McDonnell, J.J., 2004. Water Storage and Movement. In: Mckim, H.L. (Ed.), Soil Development and Properties. Elsevier Ltd., Oxford. 1253-1260.
Wesley, L.D., 2009. Behavior and geotechnical properties of residual soils and allophone clays. Obras y Proyectos, 6, 5-10.
Wesley, L.D., 2010. Geotechnical Engineering in Residual Soils. John Wiley & Sons Ltd., New York. 249 p.
Wesley, L.D., 2011. Stability of slopes in residual soils. Obras y Proyectos, 10, 47-61.
Yamusa, B.Y., Hezmi, M., Ahmad, K., Kassim, K.A., Sa’ari, R., Alias, N., Mustaffar, M. & Kassim, A., 2019. Soil water characteristic curves for laterite soil at different water contents and methods as lining system. IOP Conference Series, Materials Science and Engineering, 527, 11 p.
Yin, E.H., 1976. Geological Map of the Kuala Lumpur Area, Sheet 94, Scale 1:63,360. Directorate of National Mapping Malaysia, Kuala Lumpur.
Yusof, M.A., Setapa, A.S., Tajudin, S.A.A., Madun, A., Abidin, M.H.Z & Marto, A., 2016. The soil-water characteristic curve of unsaturated tropical residual soil. IOP Conference Series, Materials Science and Engineering, 136, 1, 1-7.
Manuscript received 26 March 2024;
Received in revised form 27 May 2024;
Accepted 1 July 2024
Available online 30 December 2024
DOI: https://doi.org/10.7186/wg503202403
0126-5539; 2682-7549 / Published by the Geological Society of Malaysia.
© 2024 by the Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution (CC-BY) License 4.0
