BREAKTHROUGH TECHNOLOGY ON CTRL

This article describes the first time a new technology was used in England for a tunnel breakthrough. On the C320 Thames Tunnels project, the breakthrough into the Thurrock reception chamber was done using glass-fiber bars (GFRP) instead of steel reinforcement for the diaphragm headwalls. That enabled the TBM disc cutters to cut through it easily in order to enter the pressurized sealed chamber inside the box and mounted on the headwall. That method eliminated the need to install a thick slurry block to prevent inundation during the breakthrough. The project is part of the Channel Tunnel Rail Link (CTRL), the largest new passenger rail construction project in England in a century, which will link the Channel Tunnel with a new station located at St. Pancras in London. The Thames tunnel project will cost $220 million to carry the line under the river. It is comprised of two 2.5 km twin bored tunnels and 1.2 km approaches. Describes the various phases of the project: manufacture of eight hybrid GFRP cages, including challenges of load transfers between the steel and glass bars; the lifting of the hybrid cages into position; the TBM drive through the soft eye; and the pressure release chamber. The final breakthrough was accomplished within a tolerance of less than 20 mm.