Excavation begins on TWDT

Excavation on Hong Kong’s Tsuen Wan Drainage Tunnel (TWDT) began in March.

Seli’s double shield TBM was pushed into the launching chamber in order to produce more room and to allow the assembly of other back-up gantries.

The project is being completed by the Maeda, CRGL, and Seli joint venture.

TWDT will be excavated in extremely strong and abrasive fresh rocks, including crystal ash tuffs of the volcanic group, the Tai Po Granodiorite, and a variety of cross-cutting dykes, including basalt, rhyolite, fine-grained granite, and quartz.

The high strength and abrasiveness of these rocks and the presence of zones of blocky and closely jointed rock will yield difficult conditions for the TBM.

Pre-excavation grouting will be required over much of the tunnel length to meet the specified groundwater control criteria.

TWDT will require, among other structures, the construction of a 5.1km long circular profile tunnel with a minimum operational internal diameter of 6.5m lined with 300mm thick prefabricated steel reinforced concrete segments.

The TBM is equipped with a robust cutting-head to cope with the hard formations and is also equipped with probe drills to investigate the rock and water ahead of the tunnel face.

The head is equipped with 47 19 inch (482mm) cutters and is powered by eight 315KW motors. The TBM breakout torque is 6600kNm.

TWDT will alleviate flood risk in the Tsuen Wan district by intercepting excess channel flow in three stream valleys to the north of this area of Hong Kong.