Tunnel’s first cross-passages completed
LATE summer saw HS2 engineers begin the task of creating cross passages between the twin bores of the 10-mile tunnel under the Chiltern hills.
A remote-controlled excavator is being used to break through and excavate them. As it progresses, a sprayed concrete lining is applied for support. This is followed by the installation of a waterproof membrane and a secondary concrete lining created using formwork.
A total of 38 passages, each 15 to 20 metres long and with a safety door at either end, will be constructed. Combined with walkways in both main bores (construction of which is approaching the half-way point) they allow passengers and train crews access to the other bore for rescue by another train in an emergency.