Construction of HS2’s longest tunnel is complete, almost five years after the works started.
Once fitted out with tracks and overhead electrical equipment as part of later phases of the project, the Chiltern tunnel will carry trains travelling at 200mph along its 10-mile route.
The Chiltern tunnel’s construction was led by HS2 Ltd’s main works contractor for this section of the line, Align JV, a joint venture between Bouygues Travaux Publics, Sir Robert McAlpine and Volker Fitzpatrick.
Main construction of the twin-bore tunnel – each to carry a single track for trains travelling north and south – began in May 2021.
As part of the project, two 2,000-tonne tunnel boring machines (TBMs) were launched from a site next to the M25 near Maple Cross in Hertfordshire.
Five deep ventilation and access shafts were sunk to depths of as much as 78m along its route and completed before the TBMs arrived.
The design of each shaft’s headhouse, by Grimshaw Architects, is intended to blend in with the surrounding landscape of the Chiltern hills.
This is the second of HS2’s five twin-bore tunnels to be structurally completed, after the same milestone was achieved for the Long Itchington Wood tunnel in Warwickshire last year.
‘Exemplary’ project delivery
Mark Clapp, HS2 Ltd head of civil engineering for the Chiltern tunnel, praised the work of the project’s contractor and subcontractors.
“Multi-faceted projects of the Chiltern tunnel’s scale and complexity don’t often come along – as a civil engineer, you’re lucky to be involved in anything like it,” Clapp said.
“The team we assembled at HS2 Ltd, and with Align JV – our main civil works contractor – and all its subcontractors, to deliver this part of the new high-speed railway was exemplary.”
Adrien Baudard, Align JV project director, added: “Being part of the successful delivery of the Chiltern tunnel has been a source of immense pride for everyone at Align and our partners across the supply chain.
“Their unwavering commitment, technical skill and collaborative spirit have been truly impressive. Whether it was advancing safety standards, setting new TBM records, or helping to train future engineers, we’ve had the privilege of learning from and working with some of the top talent in our field.
“With the completion of the Chiltern tunnel’s civil works, the achievements of this integrated project team, as well as the sustainable benefits such as carbon reduction and safety innovations, will set a standard in tunnelling for generations to come.”
