Construction News takes a tour of a mega-project with HS2 Old Oak Common project director Matthew Botelle to find out how it will be built.
Project: Old Oak Common station
Contract value: TBC
Main contractor: TBC
Station contract type: Design-and-build
Enabling works contractor: Costain / Skanska JV
Demolition and remediation subcontractor: Erith
Enabling works start: July 2018
Overall project completion: 2026
It takes us more than 10 minutes to walk from the entrance of the Old Oak Common site to the portacabin offices.
I turn to HS2 Old Oak Common project director Matthew Botelle during our journey, and tell him that I’ve never seen a site of this scale before.
“It’s a massive site,” he says, but seems unphased by the challenge.
Once completed, the new station will be 900 m long and 60 m wide. For a better perspective of its scale, you’d be able to fit four One Canada Square buildings lying end-to-end within the project’s scope.
The project will consist of a six-platform substructure, which will make up the HS2 station, as well as an overground station for Crossrail and Great Western services. The overground structure will feature eight platforms, four for Crossrail and four for Great Western services.
Proposals for HS2 phase one were first published in 2012. It included plans to build a high-speed station at Old Oak.
Royal assent was granted for the scheme’s first phase in February 2017, giving the green light for construction to start. A month later, Network Rail handed over the site (previously a train depot) and in July, demolition began after a Costain / Skanska JV won the enabling works contract for phase one as part of the south section package that covers Old Oak Common station.
HS2 Old Oak Common Station Erith CSJV 4 CGI overground
In late 2019, the JV is expected to hand over the site to the main works contractor (yet to be announced) so construction of the station can commence. Then, the big activity – creating the HS2 substructure and station platforms – can begin, according to Mr Botelle.
Mr Botelle is the man behind the design-and-build of Old Oak Common station.
Previously strategic director of TfL’s Northern line extension project and a programme director on the Dubai Metro Project, he has a collection of mega-infrastructure projects under his belt and started work on Old Oak Common station in November 2015.
A ’relatively unusual’ choice
Old Oak Common station is located just 7 km away from Euston station, which will also be redeveloped to include 11 new high-speed platforms.
It’s relatively unusual to have two stations located so close to each other on a high-speed route, Mr Botelle says. But the reason for the two close-proximity platforms is because of the opportunities for interchange.
Great Western services will pass through Old Oak station when it is completed, and Network Rail has plans to connect the Chiltern mainline to Old Oak Common.
Most critically, according to Mr Botelle, is the additional Crossrail interchange located within the station, which will provide passengers with a quick and ready link to Heathrow.
HS2 Old Oak Common Station Erith CSJV 6
Subcontractor Erith is the firm now busily demolishing the previous buildings, clearing the site and remediating the ground.
“Erith is our key supply chain member, doing the demolition and remediation and light civils works,” says JV package manager Shaun Sheppard. “We’re working closely with them.”
The tracks, which led up to the former train depot, have been uprooted and are in the process of being removed offsite.
November saw the commencement of ground investigation, with hundreds of bore holes going in to.
Mr Botelle says he has been “reassured” by the London Clay ground conditions. And because of this, the team has been able to price the job more accurately, he says. As a result, the design of the station structure has changed, cutting the estimated cost of the project.
“As we get more information we can value-engineer the structure,” he says. “We’ve taken an awful lot of cost out of the structure by utilising the [ground investigation].”
Exactly how much has been shaved off the original estimated cost of the project will not be disclosed by HS2 until the main construction contract for the station has been awarded.
Making a box
When the site is ready for construction of the station, the main contractor will begin by creating the underground box substructure, upon which the station will sit.
The box will be split into three areas: east, west, and central.
Six high-speed platforms will go in 20 m below ground at the bottom of the box in the 500 m central section. The east and west sections will contain mechanical equipment for the rail lines, including points and switches that will allow trains to access any of the platforms.
First, a diaphragm wall will be created that will outline the station while forming the main structure of the building.
The team will then create the box with top-down construction being the most likely method. “One of the benefits of doing a top-down construction is that you don’t get much noise,” Mr Botelle says. “That was very attractive to us.”
“As we get more information we can value-engineer the structure. We’ve taken an awful lot of cost out of the structure by utilising the [ground investigation]”
Matthew Botelle, HS2
This method of construction will entail the installation of hundreds of plunge columns, before the pouring of an overhead roof slab, which will act as the ground floor of the station. This will be supported by the columns.
Operatives will then excavate about 800,000 cu m of material to create the box, before construction of the box begins with the east end section.
Once this is completed, it will be handed over to SCS Railways (a Costain, Skanska and Strabag partnership), which will use this section as a launch chamber for the tunnel boring machines that will form the twin tunnels connecting Old Oak Common station to Euston.
A specially constructed tunnel will link the launch site to the former Willesden Euroterminal site located nearby so that a conveyor belt located inside the tunnel can transport around one million cu m of material offsite.
It will take “five years of massive, massive civils work” to create the tunnels between Old Oak Common and Euston, Mr Botelle says. After the tunnel boring process is over, the east section will be handed back to the Old Oak Common station team from the HS2 main civils contractor.
HS2 Old Oak Common Station Erith CSJV 7 CGI overground
Once the east section of the box is completed, this process will be repeated to construct the west end and central section of the box, with a separate chamber built in the former for a TBM launch that will begin construction of the route to Birmingham.
In the central section, three islands will be created for six high-speed platforms as well as about 44 escalators and 50 lifts.
Mr Botelle anticipates the construction of the station box will be the most technically challenging aspect of the project due to the volume of work and constraints of the site.
“There’s only one way in and out,” he said. “We’re already starting detailed logistics planning.”
The station box is expected to be completed by 2023.
When the substructure is completed, the team can begin building the above-ground station superstructure.
Adjacent to the high-speed station box, the team will build a new eight-platform station for Crossrail and Great Western main line services.
Mr Botelle estimates that work will begin in 2021.
Once finished, escalators and lifts will transfer HS2 passengers to and from an overbridge that will link to the Crossrail and GWR platforms.
A much simpler construction method will be used to create these station platforms compared to the high-speed platforms below, Mr Botelle says, with these supported on reinforced concrete foundations.
HS2 Old Oak Common Station Erith CSJV 3
Additional connectivity works will widen and lower Old Oak Common Lane, which runs alongside the site.
This is so double-decker buses can run to the station, as well as increasing the number of local buses servicing the region.
The area surrounding the conventional station above ground will be mostly green public spaces. HS2 has also signed a memorandum of understanding with DfT and Network Rail to develop a 2m sq ft triangle of land located in the south-west of the site, which will be developed in partnership with the Old Oak and Park Royal Development Corporation.
Finally, a hybrid bridge will be built from the north-east of the site, connecting the station to the surrounding OPDC developments located on the other side of a canal that runs near the station.
By 2026, the station will be completed and the first services are expected to run later that year. Construction of the station will take six years, after which 100m passengers are expected to pass through the station every year.
As Mr Botelle and Mr Sheppard give me a tour of the site, I wonder what made them decide to work on Old Oak Common.
“It’s a once in a generation opportunity,” Mr Sheppard tells me. “I can say: ‘I’ve worked on HS2’.”