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HS2 civils contracts | The technical lowdown

HS2 Birmingham Interchange visual

The government has handed out one of its biggest set of contracts to date, with the announcement of the winning bidders for the first phase of High Speed 2 (HS2) main civil works. But what is involved in the massive £6.6bn package of works?

The contract was split into seven different geographical packages, two in the south, three in central and two in the north – the ‘mythical’ N3 package is Curzon Street station.

New Civil Engineer takes a look at each of the sections and the work involved.

S1: Euston Tunnels and Approaches – SCS JV (Skanska/Costain/Strabag) – £740M

The first section of the route involves 7.4km of twin-bore tunnel to take the line north-west out of Euston in central London. Two vent shafts will need to be built at Adelaide Road in Chalk Farm and Canterbury Works in Kilburn before the line arrives at the Old Oak Common station box in west London.

The main site compound will be at Old Oak Common.

S2: Northolt Tunnels - SCS JV (Skanska/Costain/Strabag) – £1.1bn

Leaving Old Oak Common station, the route continues in the 13.5km long, 8.8m diameter Northolt Tunnel running under Ealing, Northolt and Ruislip before emerging south of a golf course in West Ruislip. The tunnel’s maximum depth is expected to be 32m below ground with trains passing through it at 320km/h.

The will tunnel require four vent shafts located at West Gate, Greenpark Way, Mandeville Road and South Ruislip.

C1: Chiltern Tunnels and Colne Valley Viaduct - Align JV (Bouygues/Volker Fitzpatrick/Sir Robert McAlpine) £965M

From West Ruislip the line runs north-west on the 190m long, in places 10m high, Colne Valley south embankment.

It continues on the 3.4km long Colne Valley viaduct across four lakes with varying environmental challenges and the River Colne. The line then passed onto the 290m long, and up to 12m high, Colne Valley north embankment.

The Chilterns Tunnel is a 15.8km bored tunnel starting at Maple Cross. It will have four vent shafts and one intervention shaft at Chalfont St Peter, Chalfont St Giles, Amersham, Little Missenden and Chesham Road.

A large site compound will be housed at the southern portal near Maple Cross. Material from the tunnel will be treated here prior to being used elsewhere on the route. The northern portal is adjacent to South Heath.

C2: North Portal Chiltern Tunnels to Brackley - CEK JV (Carillion/Eiffage/Kier) £724M

Packages C2 and C3 have similar engineering challenges, both are rural, and are made up of a mix of embankments, cuttings and a few very small sections of tunnel. The two sections are around 80km in total.

In the C2 section the line passes over Wendover Dean valley and the Marylebone to Aylesbury railway on a viaduct before entering a ‘green’ tunnel - understood to be similar to a cut and cover with grass and trees on top - to the west of Wendover.

The route passes in cutting, embankment or at surface level to the west of Stoke Mandeville and Aylesbury, east of Waddesdon and then west of Quainton to Calvert. The infrastructure maintenance depot will be located at Calvert and the line will cross over the proposed East-West rail link.

This section includes the only above ground section within the Chilterns area of outstanding natural beauty (AONB) which includes the Wendover Dean viaduct.

C3: Brackley to South Portal of Long Itchington Wood Green Tunnel - CEK JV (Carillion/Eiffage/Kier) £616M

The line then runs in a mixture of embankments, cuttings, viaducts and tunnels ending just to the north of Southam.

As the landscape becomes more urban, so the complexity increases. As the line heads north, the interfaces with motorways, railway lines and canals which ring around Birmingham will present some sizable challenges. The Delta Junction is one of the most significant.

N1: Long Itchington Wood Green Tunnel to Delta Junction and Birmingham Spur – BBV JV (Balfour Beatty/Vinci) £1.3bn

This 30km section runs from Long Itchington Wood tunnel to the proposed Birmingham Interchange Station (visual pictured above).

As one of the most complex sections, it includes 15 cuttings, 20 embankments, 1.48km of twin bored tunnel, 0.43km of single cell cut and cover tunnel, 0.63km of cut and cover tunnel, 32 highway diversions and five watercourse diversions.

It also involves building eight viaducts – including the major Balsall Common Viaduct and River Blythe Viaduct – 16 under bridges and 31 over bridges.

N1 also includes a branch off the main route from Water Orton to Curzon Street Station, known as the Birmingham Spur. This section of the line will pass through a semi-residential-industrial area and an industrial-city environment.

N2: Delta Junction to WCML Tie-In – BBV JV (Balfour Beatty/Vinci) £1.15bn

This 41.6km section runs from the Birmingham Interchange Station to tie in with the West Coast Mainline at Handsacre, Staffordshire.

It contains 21 cuttings, 54 embankments, 39 viaducts – including the major River Cole East/West viaducts and Water Orton 1 and 3 viaducts, numerous motorway crossings and highway diversions and the highly complex Delta Junction.

The Delta junction has three components: first, a 4.6km long section of the main line running south to north; second the Birmingham spur, which separates from the main line just north of the M6 and continues towards Birmingham Curzon Street Station. Third is the north chord, which joins the Birmingham spur to the main line going north.

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