Slope stability analysis at soapstone mining sites in Nyamarambe, Kisii County, Kenya

Abstract

Soapstone mining designs cause slope instability, resulting in quarry accidents causing injuries, and death to artisanal miners. Slope destabilization of soapstone strata and sliding of rock masses into open pits are common in soapstone mines. This study assessed the influence of slope angles and heights on the slope gradient, safety factor and instability of the excavated mine slopes. This paper outlines unstable slopes at the mining sites. Studies on soapstone mining in Kisii have mostly focused on socio-economic aspects but very little has been reported on slope instabilities that are common in soapstone rocks mining geosites. Kisii soapstone quarries were examined as several slope failure accidents have been encountered during mining. Field surveys made to the quarries enabled the collection of geomorphometric field data on soapstone quarries and potential slope failure zones. A digital inclinometer and tape measure were used to collect geometric data from the quarries. LEM was used to compute and analyze the factor of safety of slopes to predict the slope instability risks. The findings reveal that unsafe mining designs increase slope angles and heights, inducing instability geohazard risks. The soapstone rock mass in the opencast mines is weak and prone to slope failure. The means of slope angles and heights of the sampled quarries were 69.1° and 6.19 meters with the safety factor mean value of 0.565 indicating that all the examined quarry slopes are unstable. The results reveal that increasing slope angles and heights in soapstone mines decreases the factor of safety resulting in slope failure geohazards. The study recommends that artisanal miners should always mine under optimized slope angles and heights and suggests slope stabilization geotechniques for further scientific and academic research works. This paper provides a significant database for slope failure mitigation, sustainable soapstone mining, post-mining phaseout transformations and management.