Determination of Excavation Method and Support System for Sultan Alimuddin - Kakap Tunnel Based on Surface Geology Mapping and Excavation Face

Abstract With Samarinda serving as a key buffer to the capital city of Nusantara, which grapples with urbanization and congestion challenges, infrastructure development has become a critical focus, particularly the construction of the Sultan Alimuddin - Kakap Tunnel. Planned for Selili Village, this tunnel will be the first road tunnel in East Kalimantan and is strategically important for alleviating traffic congestion, enhancing the distribution of goods and services, and ensuring safety. However, the geological conditions at the construction site pose significant challenges, mainly due to weak rock with a high potential for landslides. By assessing the rock mass utilizing the Japan Society of Civil Engineers (JSCE) evaluation methodologies and the Rock Mass Rating (RMR), this research seeks to identify the most appropriate excavation techniques and tunnel support systems. To characterize the engineering geology, surface geological mapping, core drill analysis, tunnel excavation face mapping, and laboratory testing were performed. The RMR and JSCE assessment methods were compared to assess the rock mass quality and recommend appropriate excavation techniques and support systems. The findings reveal that the tunnel alignment is dominated by interbedded siltstone and sandstone lithologies. The rock mass quality along the tunnel, as reported by RMR, varies from fair to poor. Based on the JSCE method, the tunnel route falls into the DI, CII, and CI rock categories. The top heading and bench excavation method is recommended based on RMR, while the double bench method is suggested by the JSCE assessment. Although there are slight differences in the recommended support systems, both RMR and JSCE consistently advise using rock bolts and shotcrete as the main method of support for the tunnel.