John Craddock, contracts engineer, Ipswich Borough Council describes road repairs in Ipswich
Ipswich has a large number of concrete roads that were built in the 1960s around new housing estates, three of which had badly degraded and were categorised as in danger of imminent failure due to heavy traffic flow.
Core samples and a ground penetrating radar survey revealed that, while most road slabs were in good condition, underneath there were lots of voids as well as differential settlement caused by soil piping, whereby fine soil materials migrate down into the ground and weaken the subgrade. In some areas the slabs rocked and moved when traffic rolled over them and one road had a metre-deep ditch running underneath that had simply been bridged over with concrete.
Rather than break up the slabs and create a new road, or lay new slabs on top of the existing ones, which would have worsened settlement problems, we opted for the cheaper and less intrusive option of strengthening the subgrade and filling voids to create a level road surface.
The main challenge was to find a solution that could access the subgrade without breaking out any concrete, as the roads had to be kept open for residential access and buses.
Uretek’s system pumps a pressurised expanding polymer foam into the subgrade through 10mm holes drilled through the slab. As well as filling voids, the fast-setting material can densify and stabilise low-density compressible soils to depths of around 30 feet. Continued pumping of the material creates enough pressure to raise a slab and counteract settlement to an accuracy of +/-2mm.
Once pumped into the subgrade, the material sets within seconds — there’s no curing process as with concrete — and work is unhindered by bad weather or changes to temperature.
Using this system has allowed us to repair around 13,000m2 of road within budget. Where a full-depth reconstruction would have meant shutting the road to traffic and a long-term building programme, deep injection enabled us to allow one-way traffic and repair a section of road in just two weeks.
