Large Diameter TBM Tunnelling Beneath New Reclamation

Abstract

The Tuen Mun-Chek Lap Kok Link (TMCLKL) project successfully completed a 14 m diameter slurry mix-shield tunnel boring machine (TBM) tunnelling in Alluvium, beneath a recently reclaimed land. The in situ clayey Marine Deposits and Alluvium were subject to ongoing consolidation and creep settlements as a result of reclamation loading. This posed a challenge to the design of tunnels which needed to achieve a limiting tunnel squat of 1% of tunnel diameter over an operational life of 120 years. An innovative design was conceived by installing barrettes at the tunnel springlines to reduce the tunnel squat in the long term by sustaining the soil arching load around the tunnel. This paper presents the field performance of tunnelling with respect to TBM operational parameters. Although the barrettes were intended to reduce the tunnel squat, the field measurement showed that they also reduced volume loss ratios caused by tunnelling. The measured volume loss ratios were between 1.27% and 2.07% in the seawall area without barrettes, and smaller than 0.54% in the area with barrettes. In the seawall area, post-tunnelling consolidation settlements completed in 30 to 60 days with a magnitude of 25 mm to 30 mm for each tunnel. In the area where the tunnels were supported by the barrettes, the consolidation settlements were smaller than 5 mm for each tunnel. The tunnel squat was reduced by 40% to 50% at the tunnel section with barrettes compared to that without barrettes. Discussion is also made by comparing the measured volume loss ratios to those reported in the recent TBM tunnelling projects in Hong Kong which ranged from 0.1% to 1.2%. The TMCLKL tunnels were successfully constructed without causing excessive deformation to the overlying reclaimed platform and seawalls.