Slope Stability Analysis for Slope Geometry Evaluation Using RMR, SMR, and Morgenstern-Price Methods in Pits C2 and C4 of PT Menara Cipta Mulia Mayang Block Open Pit Tin Mine, East Belitung Regency, Bangka Belitung Islands

Abstract

Tin mining activities using an open pit mining system can affect slope stability and increase landslide risk. Slope stability analysis needs to be done to minimize the occurrence of landslides. This study aimed to determine engineering geological settings, and rock mass conditions, find slope safety factor values, as well as provide slope geometry recommendations according to the minimum Safety Factor (SF)  value criteria ≥1,25. The research area is an area with complex materials, so in this study slope stability analysis was carried out by combining rock mass classification methods through Rock Mass Rating (RMR) and Slope Mass Rating (SMR), and calculating the value of the Safety Factor (SF) using the Morgenstern-Price method with the Generalized Hoek-Brown and Mohr-Coulomb failure criteria. The analysis results obtained three geological engineering zones: meta sandstone- meta claystone, silty sandstone, and sandy claystone. The condition of the rock mass according to the RMR value, is in the moderate to good class. It has an SMR value of partially stable stability. Areas with the potential for landslides, namely STA 2 on sections B-B' with toppling type, STA 3 on sections C-C' and STA 4 on sections D-D'  with wedge type. According to the SF value, there are two unstable slopes during partially saturated conditions: sections A-A' and B-B'. The recommended slope geometry is with a minimum width of 2/3 of the height, where in partially saturated conditions, the slope has a single angle of  35 - 400, 5 m high, with an overall slope angle of 320 and 16 m high. In dry conditions, a single slope angle of 550, 6 m high with all slope angles of 370 and 15 m high.