HS2 engineers have launched a 130m-long steel bridge over the Grand Union Canal, allowing a 1.5-mile section to be reopened to the public seven days ahead of schedule.
The launch operation for Longhole Viaduct began on 4 March and involved sliding the 1,620t deck across a country road, canal and towpath near Ufton in Warwickshire.
Engineers took two days to complete the manoeuvre using the ‘skid shoe methodology’.
Two giant hydraulic jacks pushed the structure forward at speeds of up to 10m per hour, aided by special pads coated in a Teflon-like material to minimise friction during the slide.
The weathering steel viaduct, supported by two abutments and two piers on either side of the canal, was then lowered to its final position and secured.
The completion of the bridge project follows a two-and-a-half-year programme led by engineers working on behalf of HS2’s construction partner, Balfour Beatty Vinci (BBV).
Complex engineering works
At peak construction, a team of 40 worked on the project, which included the installation of 34 piles at depths of up to 30m and two concrete piers cast parallel with the canal.
The project also involved construction of two abutments, and 37 precast planks, which form the base of the bridge deck.
A new retaining wall was also built to support the structural integrity of the canal ahead of works starting.
Constructed with 7m-deep sheet piles, the new concrete-capped wall replaces the original ‘wash wall’ and soft bank, which is believed to have been formed around a century ago when the canal was previously widened.
Harry Toase, BBV’s civil engineering lead for the project, said: “The team has put in a huge amount of work to prepare for the bridge installation and shown meticulous attention to detail throughout to protect the canal and nearby Grade II-listed bridge.
“I’m delighted we’ve been able to complete the works one week ahead of schedule and thank the local community for their patience.”
Minimising disruption
Vibration levels were monitored throughout the works to protect the nearby Grade II-listed Longhole Bridge, which carries traffic and pedestrians over the Grand Union Canal between Ufton and Hunningham Hill.
Longhole Viaduct is situated 1km from the north portal of the Long Itchington Wood Tunnel. When trains emerge from the tunnel, they will travel along the Ufton Wood cutting before joining the Welsh Road embankment, which connects to Longhole Viaduct.
HS2 Ltd and BBV worked closely with the Canal & River Trust, which owns the Grand Union Canal, to prepare for the viaduct’s installation. The launch was scheduled to take place in the ‘close season’, which ends on 13 March, to minimise disruption for boaters.
Vicki Lee, senior project manager at HS2 Ltd, said: “Thanks to the hard work of our engineers and site-based teams, we’ve made good progress in this area over the last 12 months, with completion of the Long Itchington Wood Tunnel and the successful Longhole viaduct slide operation.
“There’s still a vast amount of work to do as we turn our attention to the embankments and cuttings that will link these sections of the railway ahead of track and power being installed.”
