Mechanised railway tunnel excavation and existing tunnel dismantling in the urban environment in Hong Kong

The Mass Transit Railway Corporation (MTR Corporation) West Island Line Contract 703 - Sheung Wan to Sai Ying Pun Tunnels involved the construction of two single-track tunnels from the existing Sheung Wan Station to the new Sai Ying Pun Station in the Western District of Hong Kong Island. The major tunnelling activities took place from November 2010 to November 2012, during which the two single-track tunnels of 1.62 km in total length were constructed by both Drill and Blast and Tunnel Boring Machine (TBM) methods. Approximately 794 m of the tunnels were constructed using a 6.39 m diameter slurry mixshield TBM in mixed ground conditions, passing beneath many high-rise buildings constructed in the 1950s-1980s on reclaimed land. The toe levels of the building frictional piles are located at/above the tunnel crown with a soil cover of 25 m to 30 m. An existing over-run tunnel of 5.6 m to 5.8 m in diameter and 132 m in length was dismantled using a bespoke Tunnel Dismantling Machine (TDM) to make way for the new tunnels. Extensive instrumentation monitoring was implemented to monitor the response of the ground, buildings and pore water pressures during the TBM and TDM works. This paper correlates the monitoring data with the TBM and TDM works, and compares the measurements with the predictions. Distinctions are drawn between the TBM- and TDM-induced building settlements, and between the ground and building settlements. Reasons behind these observations are explained with reference to the actual construction details and measured changes in the monitoring data. No structural distress to the buildings and structures in the vicinity had been observed.