Modelling Safety Factors of Slope Stability for Open-Pit Mining of Nigerian Tar-Sand Deposits

Abstract

Slope failure might lead to loss of lives and valuable equipment which would increase overall operational cost of running a mine. The need to have stable slopes in open-pit mining of Nigerian tar sand deposits of Dahomey Basin, Southwestern Nigeria is emphasized in this study. At Loda village, Southwestern Nigeria, samples of the laterite soil and alluvial sand which overlie the tar sand occurrence were subjected to geotechnical tests. Computer simulation of bench face angles was carried out using SLOPE/W Software to determine the bench face angle(s) with the least susceptibility to failure. Unit weight (o), cohesion (c) and angle of internal friction (0) values for the laterite soil were 25 kN/m, 45 kPa and 41 respectively for laterite. The corresponding values for the laterite, soil were 18 kN/m 3 , 0kPa and 34°. These values were used to run the software programme to simulate different bench face angles that could be cut into the two lithologic units. Factors of safety values between 3.58 and 1.73 were obtained for bench face angles between 10° and 30° which are least susceptible to failure even when inundation is considered. This research results have enabled us to recommend the use of bench slope angles ranging from 10° and 30° coupled with adequate drainage conditions which should guaranty optimum output.