Constructing the Cut-and-Cover Tunnels and Bored Tunnels of the Singapore Downtown Line

Abstract

 The Downtown Line (DTL) is a major MRT line under construction after the completion of the Circle Line in Singapore. This paper will review the ground conditions for the DTL and how the ground condition has influenced the decision on the selection of the support systems adopted for the excavation for the stations which are constructed using cut-and-cover method, and also the selection of tunnel boring machines for the bored tunnelling works. The key features of the temporary support systems will be presented in the paper and their performance will be reviewed in terms of ground movements and ground water table drawdown and its impacts. Issues encountered during the excavation, in particular for DTL Stage 2 in the soils and rocks of the Bukit Timah Granite Formation will be presented in the paper and the effectiveness of various measures implemented will be discussed based on the experience and observations during the construction. The key features and parameters of the TBM used in the projects will also be presented.