Thames Tunnel workings aerial view
Thames Tunnel north site
Thames Tunnel section
- Client
- Union Railways
- Main contractor
- Hochtief Murphy JV
- Consultant
- Rail Link Engineering
(Arup Bechtel Halcrow Systra) - Dewatering subcontractor
- WJ Groundwater Ltd
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The two approach structures for the CTRL Thames Tunnel north and south portals each involved the construction of an approach structure and a reception or launch chamber for the tunnelling machines. Overall each structure is about 430 m long, 28 m wide and up to 19 m deep. Dewatering was achieved by installing 50, 28 m deep, chalk abstraction wells. The wells were located inside the propped diaphragm wall structure so that the potentially high groundwater flows from the gravels were cut off. In order to reduce external drawdown and prevent settlement around the northern approach structure, the groundwater was recharged back into the Terrace Gravels. The design was supported by numerical modelling of the aquifer. The schemes included comprehensive monitoring utilising piezometers, flow meters, dataloggers and a remote alarm system.
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Key words
- railway, infrastructure, river gravels, chalk, deepwells, recharge