Skanska Costain STRABAG JV's (SCS JV) sprayed-concrete tunnel works have broken through into HS2's Old Oak Common station box in west London, completing a reported excavation milestone at the interface between the railway's Northolt Tunnel approach and the underground station being built by Balfour Beatty VINCI SYSTRA (BBVS).
The works comprise two approximately 360-metre-long tunnels linking the Victoria Road Crossover Box with the western end of the 850-metre Old Oak Common station box. Both connections have been excavated using sprayed concrete lining (SCL), allowing their width to increase as the railway tracks separate towards the station's six high-speed platforms.
The tunnels were mined through London Clay using tunnel excavators and lined with approximately 30,000 cubic metres of sprayed concrete. The report includes photographs of the breakthrough and comments from Rail Minister Lord Hendy, although it does not give the exact excavation date for each of the two tunnels.
HS2's published construction records provide a more detailed account of the engineering. The tunnels vary from 8.9 metres to 14.9 metres in width and pass approximately 12 metres beneath ground level. SCS JV has been constructing them since spring 2024, working alongside BBVS, which is responsible for the station structure and platforms.
Why the tunnels change width beneath Old Oak Common
The Old Oak Common connection uses sprayed concrete lining because the railway alignment requires changing tunnel geometry. HS2's published tunnel FAQs explain that the excavation becomes progressively wider approaching the station, providing room for the separation of tracks serving different high-speed platforms.
LCM calculates that the maximum published tunnel width of 14.9 metres is 6 metres greater than the minimum width of 8.9 metres, an increase of approximately 67%. The figures describe the variation in tunnel width along the alignment, not a uniform cross-section throughout the two 360-metre connections.
A tunnel boring machine would excavate a constant-diameter bore along its drive. HS2 says using one for these connections would have required excavation at the largest diameter throughout, increasing the amount of ground removed and the associated settlement risk beneath nearby roads and buildings.
SCS instead adopted cyclic excavation and support. A narrower pilot tunnel is excavated first and progressively enlarged to the required profile. Excavation proceeds in short lengths, with concrete sprayed onto the exposed ground to stabilise the opening. HS2's method includes temporary concrete faces between excavation cycles, followed by further lining and waterproofing works.
The variable geometry is particularly important at the western station approach, where the running lines must connect with the six HS2 platform tracks. The finished tunnel sections also need to accommodate the railway's permanent track, walkways and associated systems.
Ground movement controls beneath residential streets
The twin connections pass beneath the Old Oak Common Lane and Wells House Road area, including established residential properties close to the alignment. HS2's technical documents identify ground movement as a principal construction risk because the tunnel crowns are approximately 12 metres below the surface, with local variation of up to 2 metres.
The project uses continuous tunnelling where required, immediate sprayed-concrete support and monitoring of nearby structures. HS2 identifies satellite monitoring, laser surveying, prisms, targets and ground-level measurement studs among the methods used to check movement against its predictions.
One particularly demanding location is Kildun Court, above the upline tunnel. According to HS2's tunnel FAQs, the building's steel frame and pad foundations, combined with its proximity to the excavation, required specific structural protection measures. The Old Oak Common and Park Royal Development Corporation acquired the building ahead of tunnelling, and HS2 said it needed to be unoccupied while intrusive protective works were carried out.
Those measures included exposing supporting beams, installing internal structural supports and taking the lift out of service. HS2's approach to the adjacent houses on Wells House Road differed because of their brick construction and strip foundations. The published documents also describe pre-condition surveys and monitoring to assess ground movement during excavation.
The monitoring programme is relevant beyond the point of breakthrough. Ground movement can continue during subsequent lining and construction activities, while the connection must ultimately accommodate the finished railway infrastructure. HS2's technical documentation sets out the control methods, but does not publish the measured settlement results for each completed 360-metre drive.
The SCS and BBVS construction interface
The breakthrough brings together two separate HS2 civil engineering packages. SCS JV is responsible for the connecting tunnels, the Victoria Road Crossover Box and the wider London tunnelling works. BBVS is delivering Old Oak Common station, including the underground station box, platforms and associated structures.
The interface is at the station's western wall, where the mined tunnels enter the structure built under the station contract. The connection needs to match the designed rail alignment and accommodate the transition between the tunnel linings and the permanent station structure.
HS2 confirmed on 13 August 2026 that all six underground high-speed platform structures had been completed. Each platform measures 450 metres, with 1,946 precast slabs installed. Expanded, part of Laing O'Rourke, delivered the platform construction works.
That August announcement anticipated SCS breaking through the western wall of the station box. The newly reported breakthrough follows the completion of the platform structures and provides the physical western approach connection for the high-speed railway.
LCM previously examined the wider tunnelling programme in Skanska HS2 Northolt Tunnel Milestone: What London Must Watch, following completion of the Northolt Tunnel's 34 cross passages. The 360-metre Old Oak Common connections form the final approach between the Victoria Road Crossover Box and the station, with a separate excavation method and geometry.
Waterproofing and permanent lining remain part of the programme
The breakthrough establishes the reported excavation connection into the station box. Permanent lining, waterproofing and the integration of railway systems are separate construction activities within the wider tunnel and station programme.
HS2's construction FAQs describe a sequence in which a pilot tunnel is enlarged, supported with sprayed concrete and subsequently completed with waterproofing and further lining. The spring 2026 documentation anticipated concrete lining and waterproofing continuing through the programme after the initial excavation stages.
Waterproofing specialist Renesco lists the Old Oak Common tunnels among its UK project references for 2025–2026. The specialist's involvement adds a separate construction package to the excavation and station interface, although no new waterproofing contract value was announced with the breakthrough.
The eastern side of Old Oak Common is following a different excavation sequence. Two tunnel boring machines launched from the station box in January 2026 and are constructing the approximately 4.5-mile Euston Tunnel. HS2 expects those drives to finish in 2027, while construction of the station's conventional platforms, roof and building services continues.
LCM covered the separate Euston programme in HS2 Euston Tunnelling: Logistics Hard-Stops Facing London Projects, examining the overlap between tunnel excavation, utilities and transport infrastructure around the central London approaches.
How the tunnel programme has changed since 2024
LCM's comparison of HS2's dated construction records shows how the programme for the Old Oak Common connection developed before the reported breakthrough.
The HS2 work-item page last updated on 24 October 2024 said construction would finish in late 2025. HS2's subsequent tunnel FAQs, published for the later construction period, instead gave winter 2026/27 as the expected completion window, including lining and waterproofing.
The 3 November 2026 breakthrough report therefore records progress against a programme that had already been revised. It does not establish a new overall HS2 completion date or a change in the cost of the London tunnels contract. The Standard's report identifies the physical breakthrough but does not provide separate dates for the upline and downline excavations.
Old Oak Common is being developed as a 14-platform interchange, with six underground HS2 platforms and eight conventional platforms connecting with the existing rail network. HS2's wider project reset continues under chief executive Mark Wild, with the initial Old Oak Common to Birmingham railway currently forecast to open between 2036 and 2039.
The next identified works at Old Oak Common include completing the remaining tunnel lining and waterproofing, developing the railway systems interfaces and continuing construction of the conventional station above the underground HS2 platforms. The two Euston tunnel boring machines remain on their separate programme towards central London, with excavation scheduled to finish in 2027.
| LCM Project Record: Old Oak Common Tunnel Connection | |
|---|---|
| Location | Victoria Road Crossover Box to Old Oak Common station box, west London |
| Client | High Speed Two (HS2) Limited |
| Tunnel contractor | Skanska Costain STRABAG JV (SCS JV) |
| Station contractor | Balfour Beatty VINCI SYSTRA JV (BBVS) |
| Other confirmed team | Renesco (specialist waterproofing); Expanded (station platform construction) |
| Tunnel configuration | Twin upline and downline connections, approximately 360 metres each |
| Construction method | Cyclic excavation and sprayed concrete lining; pilot tunnel and progressive enlargement |
| Tunnel dimensions | Width varying from 8.9m to 14.9m; approximately 12m depth to crown |
| Stage | Breakthrough into station box reported 3 November 2026; remaining lining, waterproofing and railway systems works form part of the subsequent delivery programme |
| Programme | Construction commenced spring 2024; HS2's later published tunnel-completion forecast was winter 2026/27; Euston TBM excavation scheduled through 2027 |
| Sources | HS2 tunnel FAQs; HS2 work-item record; The Standard, 3 November 2026; Renesco project references |
How LCM calculated this
LCM reviewed HS2's Old Oak Common tunnel FAQs and its earlier work-item record on 3 November 2026. HS2 gives a minimum tunnel width of 8.9 metres and a maximum of 14.9 metres. The difference is 6 metres; dividing that difference by 8.9 metres produces an increase of approximately 67% between the two stated widths. LCM also compared the earlier late-2025 completion target with the winter-2026/27 target in HS2's subsequent technical guidance.
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