The visit is free of charge and prior registration is required. The number of participants is limited to 20 and applications will be accepted on a first-come first-served basis. For registration, please complete and return the Standard Reply Form via Email: eric.chan@arup.com. For enquiries, please contact Ir Eric CHAN at Tel: 2268 3548. Attendance certificate will be provided.

Report

Technical visit to Hong Kong West Drainage Tunnel (Western Portal)

By Carmen, Kok Man LING

On 26 September 2009, the HKIE Civil Division organized a technical visit to the Hong Kong West Drainage Tunnel (HKWDT). During the visit, Ir. Felix Poon and Ir. Thomas Yip, Resident Engineers of Ove Arup & Partners Hong Kong Ltd gave an overview of the project.

Most of the existing drainage systems of the lower catchment of Northern Hong Kong Island were built decades ago. The protection standards are no longer adequate to cope with the requirement of rapid urbanization and changes in land use over the years. During heavy rainstorms, huge flows run down to the low-lying urban areas, causing floods and disturbances to traffic and business. The HKWDT is the government’s major initiative to relieve the flooding problem in Northern Hong Kong Island, it consists of a main tunnel built deep underground in mid-level extending from Tai Hang to Pokfulam. It will collect and divert surface run-off from the upper catchment area of Northern Hong Kong Island via 34 intakes to the sea near Cyberport which will relieve the flooding hazard in the downstream build-up area.

During the visit, we went into the drainage tunnel to experience the tunnel excavation process and we were presented with the detailed construction procedures. The main tunnel excavation will be carried out by two double shield tunnel boring machines (TBM) while adit excavation will mainly be excavated by drill and blast method.  Most of the rock excavation for dropshaft will be carried out by raise boring machine (RBM) to minimise disturbance due to spoil disposal in ground level.

During excavation, the contractor will monitor ground water 60m ahead of the excavation continuously to ensure the ground water level falls into the acceptable range and will have the grouting before excavation if the ground water level is found too high. Once the tunnel is bored, the tunnel lining segment will be transferred to its position and installed instantaneously by vacuum suction method. All the tunnel segment linings have undergone the stringent quality check to ensure the quality and free the tunnel from any defect which