Geology of Tasik Pergau Jeli, Kelantan and rock slope mass rating along Gerik-Jeli Highway

Rock slope failure is a geological hazard that can endanger the human safety as well as causes the destruction of the bridge, highway, or urban houses. The excavation of rocks to build Gerik-Jeli highway had caused the instability of slopes. Therefore, Slope Mass Rating (SMR) of slope along the Gerik-Jeli highway at north Kelantan was conducted. The objectives of this research is to produce geological map of Tasik Pergau Jeli, Kelantan with the scale of 1:25000 and determine the value of Slope Mass Rating of slopes that are prone to fail through the kinematic analysis and Rock Mass Rating (RMR). Geological mapping at Tasik Pergau Jeli, Kelantan identified lithology of the study area was made up entirely of feldspathic granite. Discontinuity survey and Schmidt hammer rebound test were conducted in five respective slopes along Gerik-Jeli highway. The data collected from the discontinuities survey and Schmidt hammer rebound test were used in kinematic analysis and to determine the value Rock Mass Rating of the slopes. RMR classified four out of five slopes into Class II (good rock) whereas another slope into Class III (fair rock). Kinematic analysis showed that only one slope was unstable whereas other slopes were stable. SMR value was then determined in each discontinuities set of unstable slope. Joint set 1, joint set 2 and joint set 3 in unstable slope had SMR value of 17 (completely unstable), 43 (partially unstable), and 58 (partially unstable) respectively. The result from this research was significant in informing the citizens and engineer about the stability of rock slope at the highway so that the precaution and mitigation measures can be taken before the failure of slope.