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  Shatin Central Link – First Variable Density Tunnel Boring Machine in Hong Kong for a Shallow Tunnel Drive

  The Shatin Central link (SCL) is one of the railway projects set out in the Railway Development Strategy (RDS 2000) by the HKSAR Government and is a new rail corridor providing a direct link between the New Territories and Hong Kong Island. SCL Contract 1128 involves the construction of two sections of twin tunnels between Causeway Bay Typhoon Shelter and Admiralty MTR Station, boring underneath the densely urbanized district of Wan Chai. Challenging and variable ground conditions were specifically expected throughout the shallow alignment of the Eastern Down Track tunnel, with the geology ranging from hard rock to marine deposits and reclaimed fill. As a result, a tunnel boring machine (TBM) was required that could cope with such heterogeneous ground conditions. The main constraints for the choice were the shallow ground cover of less than one tunnel diameter giving high risk of ground settlement, slurry blow outs to the surface and the potential encounter obstructions in the reclaimed and developed areas. A Mixshield TBM was deemed less suitable and the preliminary consideration of an Earth Pressure Balance (EPB) TBM was considered to come with a certain degree of residual risk. At the Tender stage, DBJV, drawing on experience in similar densely urbanized areas, proposed a TBM capable of operating in-between slurry and EPB modes, mitigating the range of risks anticipated. As a result, the implementation of Hong Kong’s first Variable Density (VaD) TBM, with an ability to use both low and high density slurries, was chosen. In partnership with Herrenknecht and MTR Corporation (MTR), DBJV refined and improved the concept that had been used during the construction of the Klang Valley MRT project in Kuala Lumpur, where the first ever Variable Density TBM was deployed. The TBM selection and its development processes for SCL Contract 1128 were specifically designed to suit the needs of the anticipated ground conditions and to manage the project’s inherit risks associated with one of the tunnel drives.

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