RELIABILITY ANALYSIS OF ROCK SLOPE STABILITY IN OLUPI COAL MINE, ANKPA, KOGI SATATE, NIGERIA

Abstract

Loss of lives, properties and infrastructures in mines had been attributed to slope instability. The study investigated the reliability of rock slope in Olupi coal mine. The lithology of Olupi coal mine comprises of coal, laterite, and shale. The geo-mechanical parameters (discontinuity properties, uniaxial compressive strength, shear strength, frictional angle, cohesion, young modulus and poisson ratio) used in the assessment of the stability of the rock slopes were obtained from field and laboratory studies. In this research, finite element analysis method, probabilistic analysis method, and reliability analysis approach were used for three slope geometries. Phase2 Rocscience software was used for simulation of all slope geometries. Kinematic analysis of the discontinuity orientation was also done. Models 1, 2, and 3 were set up and analyzed according to the slope geometry for the mine. Strength reduction factor of 1.33, 1.24, and 1.29 were obtained from finite element analysis respectively. The slope angles were then optimized to 1.5 to conform to the minimum long-term slope stability requirement. The probability analysis of the slope for model 1, 2, and 3 were analyzed and 3.60*10-9, 9.85*10-5, and 2.22*10-9 % probability of failure was derived respectively. Furthermore, probabilistic analysis of the optimized slope angle gave 0% probability of failure. Reliability index was derived from probabilistic analysis result obtained by incorporating mean of safety factor and standard deviation of safety factor. The reliability indexes for the three models derived were 6.548, 4.706, and 6.561 respectively. Reliability indexes of the optimized slope angle gave 22.936, 22.523, and 7.704 respectively; this gives a long-term standard of safety for slope designs. In order to maintain minimum slope stability of safety factor of 1.5, a 0% probability of failure and improved reliability index, the overall slope angles for models 1, 2, and 3 should be more flat by 8º, 13º, and 10º respectively