CTRL Contract 320 forms part of Section Two of the Channel Tunnel Rail Link Project, providing a link under the River Thames between Thurrock in Essex and Swanscombe in Kent. The works comprise 2.5km of twin bored tunnels beneath the River Thames and over 1.5km of approach structures.
The 7.85m diameter tunnels were constructed using Herrenknecht slurry shield TBMs and were successfully completed fifty days ahead of schedule. Pre-cast tunnel segments were manufactured in a specially built factory on site.
The approach structures comprised significant cut and cover works, including 25m deep launch and reception chambers for the TBMs. The works comprised diaphragm walls and in-situ reinforced concrete base and roof slabs.
The existing site was marshland and a dewatering system was installed to enable construction of the approach structures. The system pumped in excess of 500 litres per second, to achieve up to 30 metres of drawdown.
The project was carried out in joint venture between HOCHTIEF and Murphy and received a Tunnel Industry Award 2003 for innovation and engineering excellence.