ABSTRACT. This study focused on the slope failures survey (SFS) along the Bundu Tuhan – Kundasang highway, which is one of the most vulnerable areas to slope failures in west coast of Sabah. The area is underlain the Trusmadi Formation (Palaeocene to Eocene age), the Crocker Formation (Late Eocene to Early Miocene age) and Quaternary Alluvium Deposits. These geologic units are dissected by numerous lineaments and structural styles produced by complex tectonic history of multi phase deformations. The tectonic complexity reduces the physical and mechanical properties of the rocks and soils; and produced intensive displacements in substrata, resulting in intensive high degree of weathering processes and instability. In this study, a total of 50 selected critical slopes were studied. This study classified the slope failures into three main groups: soil slope failures, rock slope failures and erosional failures. Failures in soil slopes (including embankments) total 34 (68 %) with 10 failures (20 %) of rock slopes and 6 failures (12 %) caused by erosion. Soil slope failures normally involved large volume of failed material compared to rock slopes, where most failures are small to large size. Of the 34 failures in soil slopes, 31 (91 %) are embankment failures making them 62 % of all types of failures. Engineering geological evaluation of the study area indicates that the slope failures took place when slope materials are no longer able to resist the force of gravity. These decrease the shear strength and increase the shear stress resulting slope failures, which is due to internal and external factors. Internal factors involve some factors change in either physical or chemical properties of the rock or soil such as topographic setting, climate, geologic setting and processes, groundwater condition and engineering characteristics. External factors involve increase of shear stress on slopes, which usually involves a form of disturbance that is induced by man includes removal of vegetation cover, vehicles loading and artificial changes or natural phenomenon. Development planning has to consider this disaster in order to mitigate their effect. An landslide risk management program should be implemented to prevent these losses. This engineering geological study will play a vital role in slope stability assessment to ensure the public safety.
KEYWORDS: Slope failures survey (SFS), failure probability, physical and mechanical properties