HS2’s tunnelling team is making significant progress as they reach the halfway mark of the 8.4-mile twin bored Northolt Tunnel between West Ruislip and Old Oak Common. This tunnel is the second longest on the new railway, with four boring machines (TBMs) working tirelessly to excavate a total of 16.8 miles of tunnel.
The first machine, Sushila, was launched from West Ruislip in October 2022, followed by TBM Caroline a month later. These machines, named after local figures such as a teacher and astrologer Caroline Herschel, are set to complete five miles of the route before reaching the Green Park Way vent shaft in Greenford.
In February, TBM Emily began its journey west from Old Oak Common towards Greenford, joined by TBM Anne in May. Together, these machines will complete 3.4 miles of the tunnel, bringing the total distance excavated by all four machines to over 8.4 miles.
Operating like underground factories, the TBMs excavate the tunnels, line them with pre-cast concrete tunnel segments, and grout them into place while moving forward at an average speed of 16 meters per day. Teams work tirelessly around the clock to support the machines both below ground and on the surface.
In addition to the tunnel excavation, other vital features such as cross passages, vent shafts, and headhouses are being put in place as the TBMs progress. The quartet of machines has already excavated nearly two million tons of earth, with the excavated material around the West Ruislip portal being repurposed to re-model a nearby golf course impacted by the tunnelling activities.
HS2 has already completed two tunnels, one stretching for 10 miles under the Chiltern Hills and another one mile in length beneath Warwickshire. Preparations are now underway to bore the final tunnel between Old Oak Common and Euston, with two additional TBMs expected to arrive in the UK this summer to continue the progress of this ambitious project.
