Second Northolt TBM gets underway in West London

Caroline begins its five-mile underground drive from West Ruislip to Greenford.

NAMED after 18th century astronomer Caroline Herschel, tunnel boring machine (TBM) Caroline began a journey under West London on October 27 that is estimated to take 22 months. Excavating the southbound bore of the HS2’s five-milelong Northolt Tunnel between West Ruislip and Greenpark Way in Greenford, Caroline was launched three weeks after sister TBM Sushila (working in the same direction to create the northbound bore), which had by this time travelled 70 metres towards Greenford.

Construction

Caroline is expected to move an average of 14 metres per day. On its journey, it will install 4207 concrete tunnel segment rings, each consisting of seven segments, which have been manufactured by Pacadar at its factory at the Isle of Grain in Kent. Spoil extracted by the TBMs will be used to create embankments for the new railway, wildlife habitats and remodelling West Ruislip Golf Course, which has been closed while the construction work takes place. HS2’s civils delivery director Mike Lyons described the launch of Caroline, the fifth TBM involved in the project, as “another significant moment for Britain’s number one levellingup project.”

HS2 Caroline, pictured on the right (with sister TBM Sushila, launched on October 6, disappearing underground to its left), began its own five-mile journey under West London on October 27, excavating the second bore of the HS2 tunnel between West Ruislip and Greenford. A Chiltern Railways Class 165 unit is pictured in the background on the Chiltern Main Line, close to West Ruislip station.