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Keltbray wins HS2 contract to assist construction of Chiltern Tunnels



Keltbray has won the contract to provide construction services for the first two ventilation shafts and head houses on HS2’s Chiltern Tunnels.


The contract has been awarded by HS2’s main civils contractor Align JV, which comprises Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.


The shafts will provide ventilation and emergency access to the 16km-long tunnels Align is digging under the Chiltern Hills.


The scope of services Keltbray will provide include:

  • Reinforced concrete works at the base of the shafts, to create a collar structure to enable the TBMs to pass through the base of the shaft

  • Internal shaft construction works to build slip-formed concrete cores and lining walls

  • Excavation and substructure construction of Head House buildings

Excavation of the first shaft to a depth of 78m located close to the village of Chalfont St Peter has already been completed, ready for Keltbray to start work.


After the construction is complete the shaft will be topped with a head house inspired by nearby barns and other agricultural buildings to help it fit into the surrounding landscape.


Below ground level, the shaft will reach down to the twin tunnels, with fans and other equipment designed to regulate air quality and temperature, remove smoke in the event of a fire, and provide access for maintenance and emergency services.


Keltbray director of strategic engineering at Keltbray Tim Lohmann said: “Keltbray is delighted to have secured this major package of rail infrastructure works with the Align JV to deliver on this important opportunity for HS2.


“The tunnels form part of the HS2 network that will help connect the country, create thousands of jobs and rebalance the UK economy. We’re delighted to be involved in such a historic project.”


Align JV has now launched both TBMs for which will dig the Chilterns Tunnels. The first of the two 2,000t machines was launched in May, with the second following around six weeks later.


Designed specifically for the mix of chalk and flints under the Chilterns, the two identical TBMs will dig separate 16km long tunnels for north and southbound trains.

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