Empirical analyses of excavation method and tunnel support system based on engineering geology of Tunnel No.8 at Jakarta – Bandung high-speed railway, West Bandung, Province of West Java, Indonesia

The Chinese Basic Quality (BQ) system was used to determine the rock mass classes and design tunnel support system of the Tunnel No.8 of the Jakarta-Bandung high-speed railway. As the BQ system is newly applied for tunnelling project in Indonesia and remains poorly understood, this research aims to determine rock mass classes at the tunnel construction site and propose the tunnel excavation method and support system alternative based on more widely used rock mass classifications of the Geological Strength Index (GSI) and Japan Society of Civil Engineers (JSCE) standard. Surface engineering geological mapping and evaluation of drill core samples were carried out to obtain accurate interpretation of subsurface engineering geological conditions, particularly the rock mass classes at the tunnel elevation. The results show that the tunnel construction area consists of very poor to fair classes of andesite breccia, tuff lapilli, and tuffaceous sandstone. The full-face method with auxiliary bench cut and multiple-bench cut method are to be applied at the tunnel sections consisting of rock mass classes CI and DII, respectively. The proposed tunnel support system is a combination of shotcrete, rock bolt, steel rib, and invert