Carrying out ground stabilisation without the need for homeowners to move out calls for clean working practices and close liaison as Uretek recently discovered in Glasgow. GE reports
Pressure on available land for new homes often calls for brownfield sites to be put to residential use. But sometimes the historic uses on those sites can impact residential developments many years down the line and resolving the issues can be challenging as homeowners are settled and do not welcome the upheaval even if the work will secure the future of their properties.
Residents on Glasgow’s Cleeves Road estate were faced with the prospect of having to leave their homes while ground stabilisation was carried out after the fill used to backfill the former quarry on which the estate was built started to subside. Glasgow Housing Association, which owns many of the properties, called in Uretek to investigate whether an easier solution could be found that would reduce disruption to residents’ daily lives.
“The houses were built in the late 1960s and early 1970s on a former limestone quarry that had been backfilled with inert material,” explains Uretek engineering project manager Dan Hadfield. “The site had suffered some subsidence issues in the past, but these were made worse when a water main running through the area burst several years ago.”
“The backfill material extends to about 18m depth and is highly variable - some is cohesive but in other areas the fill is mostly demolition rubble.”
Dan Hadfield, Uretek
There are around 300 one and two-storey houses on the estate, but only 38 are being treated during this phase of the work. “The houses have been monitored by White Young Green (WYG) and classified according to the subsidence impact,” says Hadfield.
The houses are built in rows of eight on a single 200mm thick concrete raft, which Hadfield believes has helped minimise the impact on many properties. “The backfill material extends to about 18m depth and is highly variable - some is cohesive but in other areas the fill is mostly demolition rubble, which is why thesubsidence levels are not the same across the site,” he says.
WYG’s monitoring classifies the houses as green where settlement is less than 5mm, amber where settlement levels are between 5mm and 15mm and red where the settlement exceeds 15mm. Uretek’s work focuses on the houses falling into the red category.
“Piling was precluded due the variability of the fill and the possibility of coal workings in the area,” says Hadfield. “Our solution involves injecting a resin-basedmaterial at 1m centres externally and 1.2m centres from within the properties. In total were are carrying out 900 injections at Cleeves Road.”
Uretek undertook a trial at the site in mid-August that was used to help select the mix that is being used. “The trial led us to use two mixes for this work - one is more expansive than the other,” says Hadfield.
Work on site started in September and the £1.3M scheme was due to be completed as GE went to press. “We planned which houses would be treated and when at the start of the scheme, but have liaised closely with residents to try to fit the work around them and explain the procedure,” says Hadfield. “Some residents have stayed at home and watched while we are working inside their properties, which has been an interesting situation for our teams, but the work has gone well so far.”
According to Hadfield, it was working within occupied properties that made the Uretek solution better for this site than conventional grouting as it was not only cleaner but also quicker to apply.
Although Uretek’s three pumping teams have almost finished their work at Cleeves Road, the company will be carrying out post-treatment testing to prove that the ground below the houses is now competent. WYG will also carry out ongoing monitoring of the area to check that the untreated properties do not deteriorate.