ABSTRACT. This paper describes the importance of geological engineering inputs to landslide hazard occurrences in the Trusmadi Formation slopes, Sabah, Malaysia. The Trusmadi Formation regionally consists of two major structural orientations NW-SE and NE-SW. It consists mostly of dark grey shale with thin bedded sandstone, typical of a turbidite deposit. This unit has been subjected to low grade metamorphism, producing slate, phyllite and meta-sediment as well as intense tectonic deformation producing disrupted or brecciated beds. Quartz veins are quite widespread within the joints on sandstone beds. The shale is dark grey when fresh but changes to light grey and brown when weathered. The weathered materials are unstable and may experience sliding due to high pore water pressure, steep, hummocky or rugged slopes and intensively geomorphologic processes. Engineering properties of fifty five (55) soil samples indicated that the failure materials mainly consist of poorly graded materials of silty clay soils and and are characterized by low to intermediate plasticity content (12 % to 23 %), containing inactive to normal clay (0.43 to 1.47), very high to medium swelling (7.98 to 9.28), low to high water content (5 % to 25 %), specific gravity from 2.61 to 2.69, low permeability (8.78 X 10-3 to 3.28 X 10-3 cm/s), friction angle ()from 7.72˚ to 26.65˚ and cohesion (C) from 5.11 KPa to 15.34 KPa. The rock properties of twenty five (25) samples indicated that the point load strength index and the uniaxial compressive strength range were moderately weak. The geological influence had transformed the Trusmadi Formation slopes to be highly unstable and susceptible to landslide occurrences. Six (6) related main parameters were attributed: 1) local and regional geology, 2) hydrological and geohydrological, 3) mineralogical and micro structures, 4) local discontinuities structures, 5) physical and engineering properties of soil and rock, and 6) geomorphological processes which can help in evaluating landslide problems in Trusmadi Formation slopes. In conclusion, the geological factor evaluation should be prioritised and take into consideration in the initial step in all infrastructure programmes and may play a vital role in landslide hazard and risk assessment to ensure public safety.
KEYWORDS. Geological Factors, Landslide Hazard Identification (LHI), Trusmadi Formation