Chiltern TBMs reach four-mile mark

A pair of Tunnel Boring Machines working on High Speed 2’s Chiltern Tunnel have now completed the first four miles of their 10-mile drive, reaching the Chalfont St Giles ventilation shaft from the south portal.

The milestone follows the start of the first of three tunnel drives under London in early October. More than 44,000 concrete lining segments have been installed already, with the remaining 68,000 set to be finished in two years’ time.

At Chalfont St Giles, the shaft is one of four providing ventilation and emergency access to the twin-bore tunnels. A fifth will provide emergency access only. When the ventilation shaft is complete, it will be covered by a headhouse designed to resemble local farm buildings.