Writer : Felix Tongkul
Date : 6-9 August 2006
Publisher : Proceedings on International Conference On Slopes, JKR
Location : Kuala Lumpur
Slope failures are frequent occurrences along four major roads cutting across the mountainous areas of West Sabah linking the towns of Tamparuli-Ranau, Penampang-Tambunan, Kimanis-Keningau and Sipitang-Tenom. Not until recently, geological inputs were rarely sought when designing and constructing roads on mountainous areas. This paper highlights the geological features of the mountainous areas of West Sabah and how they contribute to the occurrence of slope failures. West Sabah comprised mostly of intensely fractured, folded and faulted Paleogene sedimentary rocks of the Crocker and Trusmadi Formations with minor occurrence of igneous and metamorphic rocks. The Crocker Formation consists of sandstone and mudstone whereas the Trusmadi Formation consists of meta-arenites, slates and phyllites. The mountains of West Sabah which rises up to an average height of about 2500 m evolved as a result of NW-SE tectonic compression related to subduction-collision of an oceanic-continental lithosphere under Sabah that began about 40 million years ago. Based on a detailed geological study of slopes along Kimanis-Keningau road, four main sources of slope failures were recognized, one, related to intensely sheared mudstones within a localized fault zone; two, related to unfavorable orientation of discontinuity planes whereby bedding and joint planes of sandstone beds occur parallel or sub-parallel to the slope face; three, related to the presence of intensely fractured and sheared sandstone and mudstone beds within a regional fold hinge; and four, related to the presence of old landslide deposit.