Two of HS2’s large tunnel boring machines are to be buried into the site at Old Oak Common next year so they can wait there until a decision is taken about how to build Euston station.

The two tunnel boring machines (TBMs) are needed to dig the two railway tunnels linking Old Oak Common to Euston, but when construction of Euston station was paused earlier this year, there was also the decision taken to delay the two connecting tunnels as well.

Although there’s no practical reason that delaying the Euston station build would require the two connecting tunnels to be delayed, with Euston station effectively on lockdown at the moment it would require the station site to be partially reopened to allow the tunnel portals to be constructed for the TBMs to arrive.

HS2 has also said that delaying work on the Old Oak Common to Euston station tunnels allows them to focus on the section up to Birmingham. There’s also a vanishingly tiny chance that the tunnel’s alignment could be changed to meet up with a redesigned Euston station.

So the two tunnels are also on hold, but to reduce disruption when the two tunnels do start being built, HS2 will drop the two tunnel boring machines into position at the eastern end of Old Oak Common station in readiness for when they are needed.

The two tunnels were expected to start being constructed next year, and as there’s a long lead time on ordering the TBMs, they will be arriving anyway, and installing them into the underground chamber where they will be needed also reduces the headache of storing them somewhere else and then assembling them later.

Placing the TBMs in situ also avoids disrupting Great Western mainline railway in the future, as it will widened as part of the station build, and happens to be running over the top of where the underground chamber needs to be built.

Although it sounds like a major intervention in the plans, and while it is unusual to put a TBM in the ground and leave it there, it’s not unusual to build empty concrete boxes in the ground years, or even decades before they’re needed.

When the Elizabeth line was being built, it made use of the Moor House shaft which was built in 2004 specifically for Crossrail, even before Crossrail was given approval in 2008. There’s also a space under an office block in Victoria ready for when Crossrail 2 opens, and plenty of other examples of holes in the ground being built long before they are needed. All because it’s considerably easier and cheaper to build them early and leave them empty than build them later*, and if they aren’t needed, then there’s a large empty space that will find a commercial use anyway.

The government has committed to opening the extension to Euston, so the TBMs will be switched on. Eventually.

Meanwhile, work carries on to complete Old Oak Common station, with six platforms for HS2 trains and eight at the surface for mainline and Elizabeth line services. Also, an ex-Crossrail tunnel boring machine is about to start digging a tunnel next to the station so that spoil removal and deliveries can arrive without using the roads. Although always required, the logistics tunnel will have added value when the Euston tunnel works start as they will be able to minimise the disturbance to the fit out of the Old Oak Common station.

When Old Oak Common station opens in 2029-33, as it will be the terminus, it’s expected a large percentage of HS2 customers will switch to the Elizabeth line, and TfL is in discussions with the government to secure orders for additional Elizabeth line trains to cope with the large influx of extra passengers.

The date that a modified Euston station will eventually open is not known, but it’s now not expected to be until 2040 at the earliest.