Intrusive surveys undertaken after the discovery of a suspicious object resulted in crucial insights into extremely complex ground conditions, and the creation of a solution to an unexpected piling problem, which enabled a construction company to keep a project on track
Workers from McTaggart Group were clearing a 22-acre brownfield site on the Dalmarnock Riverside project in Glasgow, ready for the construction of 562 new homes, when a worker spotted something suspicious. As per site protocol, work stopped and the site supervisor was alerted.
The team photographed the object from a safe distance and sent the images to SafeLane Global, an unexploded ordnance (UXO) company McTaggart had previously worked with. During project planning, no one had anticipated encountering buried unexploded ordnance on this former factory site.
SafeLane's technical field manager and explosive ordnance disposal expert Nigel Barton MInstRE was able to identify the object as a WWII anti-aircraft shell. Speaking about the find, the former Royal Engineer explains: "It's a common misconception that only London and the south-east of England were extensively bombed. In truth ports, key infrastructure, and factories were targeted across the length and breadth of the UK."
The Royal Navy attended the site immediately and safely disposed of the shell in situ, enabling construction workers to get back on-site within hours of the find.
Following the unexpected find, McTaggart project manager Stuart Cuthbertson requested a threat assessment be carried out to determine the danger posed by further unexploded ordnance on the site. The following survey showed that the site was at a medium risk of further contamination and Cuthbertson retained SafeLane to provide complete clearance.
"I was unwilling to expose my guys to risk and I was not prepared to jeopardise the timelines and success of the project," says Cuthbertson
To ensure the site was safe, SafeLane's methodology provided an intrusive survey solution conducted using rigs to drill boreholes. Non-ferrous tubes and probes were then inserted into the holes. The probes recorded live data which was processed and analysed on-site in real-time, and cross-checked for quality assurance by a team of geophysicists in SafeLane's Kent offices.
Surveying began within four weeks of the UXO find and took 17 weeks to complete. In total, 1,300 surveys were undertaken and while no further ordnance was identified, the process revealed multiple obstructions including: steel girders, reinforced concrete and cavernous spaces. All of these would prevent the traditional piling operations McTaggart had planned.
SafeLane Global, which has over 30 years' experience in UXO risk mitigation and can just as easily use its rigs to probe pile positions as it can for intrusive surveys.
Speaking about the surveys, Cuthbertson says: "Ironically, if we hadn't found the UXO we could have been delayed further, as the probing carried out gave us a much better understanding of ground conditions on-site - much more comprehensive information than we got from the original site investigation.
"The time and money spent at the front end of the works because of the UXO ended up saving us time and money in the long run because we could keep SafeLane's rigs on site to drill all the pile positions where traditional piling would fail."
At certain points, the ground conditions were so difficult that drill bits designed to last at least 1,000 - 1,500 drilling metres were only lasting two to three metres. Speaking about conditions and keeping up with demand, Duncan Mackenzie from Epiroc, which supplied the bits, says: "This was a unique situation we all found ourselves in. But working closely with the client, the manufacturers in America and our air freight company we were able to keep up with demand."
SafeLane's bespoke intrusive survey methodology has been developed to provide the most accurate results possible. The drill rigs utilised are useful tools for identifying any obstruction that could impact the ability to complete a project on time.
SafeLane Global has a CIRIA C681 unexploded ordnance flowchart to help contractors manage UXO risk assessment.
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