ABSTRACT
The Tuen Mun-Chek Lap Kok Link successfully completed a 14 m diameter slurry mix-shield tunnel boring machine tunnelling in Alluvium, beneath a recently reclaimed land. The in situ clayey Marine Deposits and Alluvium were subject to on-going consolidation and creep settlements under the reclamation loading. This posed a challenge to the design of the tunnels which needed to achieve a limiting tunnel squat of 1% of tunnel diameter and a long-term settlement of 500 mm over an operational life of 120 years. An innovative design was conceived by installing barrettes at the tunnel springlines. The barrettes reduce the ground settlement and tunnel squat by sustaining the arching load around the tunnel. This paper presents the design methodology of tunnel construction by using finite element analysis. The predictions were compared to the field measurements of ground settlements. The strength gain in the clay layers due to consolidation and the barrettes were found to reduce the ground settlement caused by the tunnel excavation.
