ABSTRACT
The Circle Line (CCL) is a circular rail line linking the North-South, East-West and North-East lines to the city in Singapore. The line comprises 33 stations, of which 30 have been completed and came into operation in phases from 2009. Circle Line 6 (CCL6) projects will add the remaining 3 stations namely Keppel, Cantonment and Prince Edward Road stations as well as an extension of Kim Chuan Depot, closing the loop for the CCL. Due to delays affected by COVID-19, CCL6 will be completed in 2026 and the overall connectivity of the Mass Rapid Transit (MRT) network in Singapore will be enhanced, with commuters enjoying a direct route from areas in the Western parts of Singapore to key employment areas in the Central Business District and upcoming developments in downtown Marina Bay area.
To construct the tunnels in the densely urbanised environment, 3 Earth Pressure Balance (EPB) Tunnel Boring Machines (TBMs) were used for the 4.4km of tunnelling works, which would link the 3 new stations to the rest of the existing operational CCL.
There were several critical undercrossing of structures by the TBMs. One of the TBM undercrossed live vehicular viaducts. The viaducts had to be underpinned prior to the TBM mining through the detached piles. Throughout the duration of the works, the road remained operational and opened to traffic. Another TBM undercrossed residential, commercial properties, live sewer, water tunnels and a national monument (a former Railway Station). Protection works were carried out on key heritage elements and over 600 instruments were installed to monitor the building during the tunnelling works. This paper details the tunnelling challenges faced and how they were successfully circumvented.
