Main contractor Galliford Try is using an innovative tube canopy system for construction of the subway. Pipe jacking, which would ordinarily be used for this type of work, was ruled out because it did not provide sufficient control of settlement to allow trains to continue running above.
Initially, the team excavated a pit for the subway on the northern side of the line to account for the four-metre difference with the level at southern end of the subway. As part of this process the retaining walls above the pit were strengthened with temporary works in the form of a 16-tonne torsion beam to prevent lateral and rotational movement.
Next a series of 30 steel tubes, of 610mm diameter, were driven horizontally and clutched together to form a goalposts structure through the embankment below the railway line. They were then grouted. Each tube is 27 metres long in total, comprising 12 two-metre lengths and one three-metre length. The augur was mounted on a giant thrust control frame capable of providing a firm base for exerting the 80 tonnes of hydraulic pressure required. The area within the goalposts was then excavated and, as it progressed, intermediate frames were placed at one-metre centres. Now fully excavated, the subway is being lined with concrete and a concrete slab cast.
Galliford Try operations manager Ian Woodall said: “It’s relatively unusual in the UK for a rail scheme to feature the tube canopy system and our use of it at Newton-le-Willows has attracted the interest of the rail sector.”
As well as the new subway beneath the station to connect its halves the £18m project for Merseytravel includes new lift shafts to provide step-free access and a new ticket office and waiting areas.
The £18m scheme has been funded through the government’s local growth fund and forms part of the Liverpool City Region Combined Authority long term rail strategy. Completion is set for late summer.