Surface and subsurface engineering geological mapping for empirical designs of excavation method and support system of Tunnel 6 of Jakarta-Bandung high speed railway, Indonesia

Abstract

Empirical design of support system at the Tunnel 6 of the Jakarta – Bandung high-speed railway was based on the Basic Quality (BQ) system, which had not been adopted in Indonesia. This research was carried out to better understand the rock mass quality at the tunnel construction site by comparing rock mass quality determined by the BQ system to that determined by two more popular rock mass classifications, namely the Geological Strength Index (GSI) and Rock Mass Rating (RMR). Surface and subsurface engineering geological mapping were carried out and tunnel excavation method and support system were proposed. The engineering geological model of the BQ, GSI, and RMR systems showed that the sedimentary rock masses of the Miocene Jatiluhur Formation generally had poor to very poor quality, while those of the Quaternary Volcanic Formation had very poor to good quality. Based on the RMR, the stand-up time values of the sedimentary rock masses were predicted to be relatively low as compared with those of the Quaternary Volcanic Formation, implying requirement of a relatively quick support system installation after excavation. In general, a combination of systematic bolt, shotcrete and steel ribs is the recommended support system for this tunnel.