On 28 February, 2016, the launching ceremony of the Rectangular TBM independently designed and manufactured by China Railway Equipment Engineering Group (CREG) was hosted in Singapore, marking the first use of specialty shield machines in the country.
The Chinese TBM will be used to excavate the running tunnels between stations of the 43km Thomson-East Coast line. According to the New Civil Engineer (NCE), as two of the stations Havelock and Stevens are in a congested central area, the Land Transport Authority and its Contractors decide to use a rectangular cross section TBM for passenger underpasses to improve construction productivity.
Generally underpasses are supposed to be built in cut and cover. Yet given the fact that this would have involved ground treatment to control settlement, as well as protecting and diverting utilities and installing piles and beams to support the excavation, the Singapore Authority began to look for trenchless technologies that could excavate lengths of up to 150m in soft soils at shallow depth, and eventually found two possible rectangular TBM options in Japan and China.
NCE said, although both machines are suitable for soft and homogeneous ground, the Authority prefers the rectangular TBM from Chinese supplier CREG to the Japanese machine in that the latter requires a minimum overburden of at least 1.5 times the depth of the excavation which is not the case at the Singapore sites.
Compared to the round cross section machine, Rectangular TBM can improve the space utilization rate by 20%. Its entry into Singapore has caught wide attention in the country. This is the first attempt for the Singapore Authority to introduce large cross section rectangular TBM and therefore is of great significance for the country’s underground construction development and the similar projects in the future.