The sheer size and scale of the operation to build the Old Oak Common High Speed 2 (HS2) station has emerged in an exclusive interview with HS2 Ltd project director S4 Old Oak Common Matthew Botelle.
The HS2 station at Old Oak Common will be the last stop before the £56bn high speed rail line terminates 6km to the east at Euston, in central London. Passengers using HS2 phase 1 route between London and Birmingham will be able to disembark at Old Oak Common and interchange with Crossrail’s Elizabeth line and the Great Western Railway (GWR). The station will have a capacity for around 100M passengers, rivalling Waterloo Station in Central London.
Trains from the east will arrive at underground platforms from the Euston tunnels section and head north via the Northolt tunnels.
Each of the six new platforms for the high speed line will be 400m long. To accommodate the switchings and crossings at either end of the platforms, the station will include a huge underground box spanning the length of the tracks. This will be a total of 903m long, 70m wide and 15m high in the west to 22.5m high in the east.
“It’s one the biggest structural boxes in the world,” said Botelle. “Certainly nothing will be built on this scale ever again in Britain,” he added.
From the HS2 platforms around 16m underground, passengers will ascend to a 150m by 70m by 21m concourse in the surface level station. This will then link through to the adjacent Elizabeth line and GWR station and platforms.
Although the structure of the underground box is relatively simple, work will be complicated by the logistical challenges of the constrained site, the sheer volume of material to be removed and the interface between the three different lines, said Botelle.
Around 1M.m3 of material from the box and 2M.m3 of material from the tunnels on either side will have to be removed from the site, he said.
“It’s a logistics challenge,” he said “It’s essential we get the excavated material out by rail and conveyers, so that’s why it’s essential the strategy gets nailed down as soon as possible.”
To add to the challenge, the ground at the site is contaminated resulting from 103 years of industrial use. As a result it will have to undergo a major remediation programme.
There will also only be one entrance and exit to site via the south west corner, through a GWR rail depot. This is currently being decommissioned to make way for the new stations.
Botelle said first works will incude widening and adjusting the alignment and the size of the access road so trucks and the demolition equipment can get onto the site.
Plans are for the station box to be constructed with diaphragm walls around its perimeter, and a large concrete and bentonite slurry plant will be located on the site.
The sub-surface HS2 station will also be mechanically ventilated, allowing a much taller adjacent site development to be built.
“If you build above a certain level on the surrounding plot of land, you get dead air over the box because of the prevailing wind direction,” Botelle explained. “If you mechanically ventilate the box, you’re not affected by cross winds and you can build higher buildings on the adjacent plots.”
Old oak Common Station
To allow the new stations to be built, the decommissioning of the GWR and adjacent Heathrow Express depot is being carried out in four phases. As these are completed, more land will be released to HS2 for track, platform and and station construction.
Phase one included the removal the tracks serving the depot from the main Network Rail signalling system. The data transfer was completed at Christmas last year and this stage has now been completed.
Phases two and three, are due for completion in summer this year and next year. These include demolition of the Heathrow Express depot, allowing the HS2 station and interface building to be built. In phase four, planned for completion in 2020, the adjacent Heathrow Express depot will be demolished making way for the Elizabeth Line and GWR tracks and platforms.
Phase four works is directly to the north of the existing GWR tracks, so to save time and ease construction, six out of the eight platforms for the Elizabeth line and GWR will be built off site and lifted into place during possessions. The remaining two platforms which are directly adjacent to the existing GWR tracks will then be constructed in a more complex, staged sequence.
Despite the Elizabeth line opening at the end of this year, trains will not stop Old Oak Common station until it opens in 2026. Botelle wants the station to set standards for design with big, light, open spaces, excellent way finding and prominent lifts and escalators, making it easier for passengers with luggage to move around.