【Introduction of the project】
The Thomson Line was the 6th underground Mass Rapid Transit (MRT) system which consisted of 22 MRT stations and its total length was an approximately 30km. Furthermore, it is expanded along the North-South corridor and eastwards along east coast of approximately 43km which is called “Thomson-East Coast Line (TEL)”. Finally, TEL consists of 31 MRT stations and an integrated MRT cum bus depot at Mandai.
There are two existing MRT Lines, North South Line (NSL) and Circle Line (CCL) currently operating within the proximity of the construction area of the new Marina Bay Station T226. A new Underground Pedestrian Linkway (12.5m(W)x40m(L)x6m(H)) which leads to the existing Marina Bay Station for NSL and CCL is constructed directly underneath NSL tunnels by means of Open Faced Rectangular Shield Machine with the cutting of existing NSL piles and subsequent Underpinning Works. Two new Railway Tunnels aligned vertically are constructed just underneath this Linkway by Sprayed Concrete Lining (SCL) method.
The soil profile in the Marina Bay area includes reclaimed Sand Fill at the surface, very soft clay so-called Marine Clay of part of the Kallang Formation Stratum which has 0 to 3 of SPT ‘N’ Value and consolidated Sandy Silt so-called Old Alluvium (OA). In order to excavate such a soft clay safely by Open Faced Rectangular Shield Machine, the Horizontal Jet Grouting Pile (JGP) is adopted under the existing tunnels where the Vertical JGP cannot be physically installed. Ground Freezing Method is implemented to cut off the underground water through OA for safe excavation of lower SCL Tunnel. Ground Freezing method is used for the first time for a railway project in Singapore.
Such Japan-based Technologies were fully introduced and implemented from the viewpoint of both design and construction and these complex works are completed successfully and safely owing to the combined efforts of the three professional parties, namely the Design and Construction with the Instrumentation & Monitoring Teams.
The above civil engineering technologies / experiences in T226 Project will contribute to not only further deep and complex underground infrastructure system in Singapore but also other Asian countries which demand urban infrastructure development by applying advanced use of underground spaces.