ASSESSMENT OF ROCK SLOPE STABILITY USING ENGINEERING ROCK MASS CLASSIFICATION IN SELECTED QUARRIES SOUTH-WESTERN NIGERIA

Abstract

Rock slope stability is a challenging task in geotechnical engineering because it has to do with safety of life and property. Therefore, this study assessed the rock slope stability using engineering rock mass classification in three selected quarries in Oyo and Ogun states, Southwestern Nigeria. The objectives of the study were achieved through detailed field measurements of the discontinuity parameters carried out on igneous, sedimentary and metamorphic in-situ rocks at FW San He Concept Limited granite quarry and Lafarge Ewekoro both in Ogun State and Marlap Nigeria Limited, Igbeti in Oyo State. Two rock samples from each quarry were collected for the laboratory determination of the rock density and Schmidt hammer was also used to measure the hardness of the rocks. The uniaxial compressive strength of the selected rocks were obtained from the Schmidt rebound hardness values and densities. Stereographic plots of the dip and dip directions were also carried out using stereoware software. The Rock Mass Rating (RMR), Geological Strength Index (GSI) and Slope Mass Rating (SMR) were obtained from results of field work, stereographic plots and laboratory experiments which were then used to assess the stability of the rock slopes in the selected quarries. Granite and marble has RMR of 65 and 64 respectively and both adjudged good rocks while limestone has RMR of 42 and adjudged fair rock. Granite has GSI of 78 and is described as a very rough fresh unweathered rough rock, limestone has GSI of 58 described as smooth moderately weathered or altered surfaces while marble has GSI of 74.5 and is described as having smooth, slightly weathered iron stained surfaces. Granite has SMR of 61.81 with stable rock slope, limestone with SMR of 32.17 has unstable rock slope while marble rock with SMR of 55.89 has partially stable slope. From the results obtained, only Lafarge limestone quarry has unstable slope based on low SMR value. Hence, the study has provided a relatively quick means of information gathering of the selected quarries and a means of ensuring the safety of workers and equipment in the quarries.