STABILITY ASSESSMENT OF ROCK SLOPES FROM RANAU, SABAH USING MODIFIED D-SLOPE METHOD

Abstract

An assessment of stability potential of rock slopes from Ranau, Sabah has been conducted using modified D-slope method. D-slope comprises of G-Rating determination and Potential Instability to assess the slope condition using field observations, laboratory analysis and microfabric analysis. 17 parameters have been done for G-Rating purpose including the type of rocks, weathering grade, existence of faults and joints, number of major sets, number of orientations, aperture, persistence and spacing of discontinuities, rainfall, hydraulic condition, height of slope, history of instability, porosity, strength, micro-petrographic and micro-fractures index. Kinematic analysis is used for Potential Instability analysis to determine the type of failures for each slope. This later is to determine the level of slope’s risk: No Risk, Low Risk, Moderate Risk or High Risk. Six slopes have been chosen from Trusmadi Formation and ultrabasic Rocks along Marakau – Ranau Sport Complex. Based on the results of G-Rating, only slope S1 and S4 have value more than 0.4 while other slopes have less than 0.4 which indicates stable slopes. Based on kinematic analysis, all slopes experienced wedge failures with S4 and S5 also have planar failure possibility which show that all slopes have potential instability. D-slope analysis indicates that slope S4 is considered as Moderate Risk with mitigation suggestions are rock anchor and soil nailing with further actions required. Slope S1 is categorized as Low Risk with suggestions of stream system inspection and vegetation on exposed area of the slopes, while other slopes (S2, S3, S5 and S6) have no suggestion for mitigation as been assessed as No Risk.

Keywords

• D-slope method
• laboratory analysis and microfabric analysis
• Trusmadi Formation
• G-Rating
• Potential Instability