The current package of work involves the construction of the 4nr Chiltern Tunnels’ porous portals. One porous portal is made up of 2nr 500m stamped concrete wall from 4.5 to 7.4m high and 1nr 500mm thick curved concrete roof (inner diameter of 4.55m). There is one 240m and one 160m long portal at each end of tunnel (16km apart). Specific formworks have to be designed and supplied, allowing portals realisation while TBMs are boring and supplied.
The package includes also the North Portal base slab (thickness 2m x 5700 m2), the South Portal base slab (2m x 2250 m2), the North break out preparation works, 2nr cross passages and concrete footpaths.
The successful Subcontractor will be expected to work and liaise in close proximity to the Main Contractor’s TBM teams and other trades. Proposals will be required to include construction methodology, equipment selection, temporary works and any access arrangements to service the works. These works are planned to commence in November 2021 and will be completed by mid-2025.
Selection will depend upon the technical and commercial submission. Contractors will meet a high standard of health, safety, quality and environmental requirements.

The package will be competitively tendered and assessed against a split between commercial (price) and non-commercial/technical criteria – The intention of the Contractor that these works will be tendered as 1 enquiry, however we reserve the right to split the works and award the package to more than 1 sub-contractor – we do not anticipate this award being to more than 2 contractors.
In July 2017, ALIGN (Bouygues Travaux Publics, Sir Robert McAlpine and Volker Fitzpatrick) won the significant C1 package of the UK High Speed 2 line (HS2). Lot C1 consists of 21.6km of high speed rail infrastructure in a rural environment. This will include a 3.37km viaduct, 15.75km twin-tubes tunnel and five vent shafts handling both piston effect and tunnel ventilation.