Infilling work on a Victorian tunnel with a tragic past has been completed by contractors working for the Historical Railway Estate (HRE).
AmcoGiffen has finished a three-month programme at Clifton Hall Tunnel in Pendlebury, Greater Manchester. The tunnel gained notoriety in the 1950s when the collapse of a construction shaft resulted in five fatalities. Four houses on the street above were also lost.
Afterwards, the tunnel was closed and partially infilled but a few voids were left that have now been filled to ensure the tunnel remains safe.
HRE engineer Andrew Willison said National Highways took over managing the HRE in 2013 and had carried out regular safety checks at Clifton Hall.
“We decided to fill the remaining voids as a precautionary measure and to ensure the site remains safe,” he said.
Before work started, AmcoGiffen lowered a cavity auto laser scanner into drill holes to provide 3D images of the voids.
AmcoGiffen contracts manager Dave Martin said the technology was new to the company as there were few scanners in the UK.
“The imagery helped us to calculate the volume of materials required to fill areas of the tunnel with voids present, one of 200m long and the other 150m long,” he said.
“Both sections had five holes drilled that we used to insert the cavity scanner and to pump the materials during the filling stage. In total 2,200 tonnes of material were needed to fill the voids.”
A mixture of cement and fly ash was used in the voids as cement alone would be too strong and would not flow far enough, as it needed to travel 30m. Fly ash, made from combusted pulverised coal and added to the cement to increase workability and durability, also meant waste was reduced.
Pumping the materials during the filling stage took 10 weeks, working day shifts to keep noise to a minimum for residents.
Some of the drill hole locations were changed to help protect trees and the access areas have been reseeded.
Constructed in 1846, Clifton Hall Tunnel is a 1,187m-long double track horseshoe-shaped tunnel lined with brick. Its construction was difficult from the beginning as the ground was very unstable where mining had already taken place.
The surrounding area was subject to intense urbanisation. Homes were built directly above the tunnel and there were several rounds of remedial works, including the addition of steel ribbing to provide additional support.
Following a partial collapse on April 13, 1953 all trains were stopped and inspection carried out. Two weeks later the tunnel roof failed, directly beneath an old construction shaft.
Residents described hearing a loud cracking noise at 5:35am, followed by two houses collapsing. The tragedy resulted in five fatalities and the tunnel was never reopened.
