Half of the cross-passages on High Speed 2’s ten-mile-long twin bore Chiltern tunnel have now been completed.
19 of the 38 cross-passages intended for use for emergency evacuation have now been excavated using remotely controlled mini excavators. Digging starts on the southbound running tunnel, with between 15 and 20 metres of excavation needed to link with the northbound running tunnel. The ground is supported with sprayed concrete lining before a waterproof membrane and then secondary concrete lining are installed.
Temporary seals for fire safety are installed on the cross-passages, awaiting delivery of permanent safety doors from Bolton-based Booth Industries.
Breakthrough by the two tunnel boring machines at the north portal is expected in early 2024.
The works are being undertaken by the Align joint venture formed of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick, which is also responsible for the Colne Valley viaduct, now also at its halfway point.