It was already a race against time at Stevenson Road – when the CML team discovered three UXOs (unexploded ordnances)
When we started work installing a 30m x 6m rock armour scour protection blanket below the river bed around the central pier of Stevenson Road Bridge in Sheffield, we were already facing time constraints due to the environmental protection of the marine habitat and the disruption that would be caused by closing the very busy Trans Pennine trail walking route.
We planned to start work earlier in the year but following meetings with Sheffield City Council and the Environment Agency we finally got the go ahead to commence works after the August Bank Holiday 2018. The issue now was the increasing risk of rising water levels in the river Don caused by Autumn rainfall which could impact on the successful completion of the project.
The team were almost three weeks into the works, having installed the access ramp leading into the river and completed 50% of the rock armour blanket, when they exposed three UXO’s (unexploded ordnances) whilst excavating underwater around the upstream nose of the pier. This was a first for all of us and we informed the police, who immediately cordoned off Stevenson Road and alerted the bomb disposal team, who came and removed the material.
We were obviously interested to discover what we had uncovered but were told that due to the ordnances’ condition they weren’t able to determine exactly what they were.
This resulted in our works being delayed while UXO clearance specialists were consulted on how best to continue the works without danger to the public, the workforce and the surrounding infrastructure. By now the trout spawning season being only weeks away seemed a minor issue but the necessary permissions still had to be granted.
Fortunately, the Environment Agency granted a short extension to our permit allowing us to complete the work so the site team were just left with the threat of digging up further UXOs and the prospect that rising river levels would create difficult working conditions.
We continued with the excavation using an armoured eight tonne excavator working alongside two specialist UXO clearance engineers whose job was to excavate and test the excavated material for any potential further findings.
An emergency road closure was put in place, stopping all vehicle and pedestrian movements on Stevenson Road Bridge during working hours, and with the high pressure gas pipe attached to the outside of the bridge feeding local businesses, the only feasible option was to reduce the pressure and have engineers on site in case the gas needed to be shut off in an emergency.
The scour protection works within the watercourse were completed with no further UXO’s found and the team managed to remove the GeoDam, access ramp and reinstate the footpath by the end of October to the delight of the local council and the Environment Agency.
As part of the temporary works permit arrangements the Environment Agency required the working area to be isolated from the rest of the watercourse to protect the marine habitat from increased disturbance and silt contamination. CML employed the use of a geotextile silt curtain and a GeoDam. The GeoDam is a water inflatable temporary damming solution, constructed from a woven geo-textile material outer sleeve and two polythene or PVC tube inner liners. When filled with water the dams create a hydro-static water tight seal using the weight of the water within the polythene tubes.
Mark Osborne, Network Rail Site Manager, recognised the difficulties faced. “On behalf of Network Rail, please pass on my thanks to all involved. A well organised and managed project, maintaining high standards on what’s been a challenging project. “