An Innovative Design of Retaining Wall in Lung Shan Tunnel Construction

The Heung Yuen Wai Highway opened on 26 May 2019. The 4.8km Lung Shan Tunnel, as one of the main sections of the Heung Yuen Wai Highway, is the longest land-based road tunnel in Hong Kong.  It was a success after 5 years of efforts by the project team. Most of tunnel excavation commenced at its Northern Portal near Princess Hill where a mega-sized tunnel boring machine was launched. The original design of the Northern Portal required 3m diameter bored pile walls for supporting a slope cutting to reach the invert level of the tunnel. Early completion of the portion formation works would be essential to accelerating the overall construction programme for the project. An innovative design involving composite retaining walls and gravity wall with sloping wall backs was proposed to replace the bored pile walls to enhance the programme and improve works quality. The composite wall involved installation of a soldier pile wall temporarily supported by tie-backs. Upon reaching the final excavation level, the soldier pile wall was integrated with a reversed L-shaped R.C. wall to form a permanent composite wall with a maximum retaining height of 29.33m under the temporary stage and 20.975m under the permanent stage for supporting the cut slope behind the wall.