Uretek displayed the fine art of expert ground engineering with the successful strengthening of soil under the National Gallery of Ireland in just three days.
The UK arm of the Finland-headquartered firm used geo-polymer injections to allow main contractor John Paul Construction to continue with the reconfiguration of the Dargan and Milltown wings of the Dublin institution.
Uretek, which is increasingly being called in at the design stage of major projects, due to the time-saving ground strengthening technique, published a paper earlier this year documenting how engineers can benefit from the technology.
“On the National Gallery of Ireland, changes to certain areas of the building meant additional loading acting upon existing foundations,” says project engineer Liam Bromley. “Upon reviewing site investigation data, it was deemed that the soils underlying these foundations did not possess sufficient bearing capacity.”
Traditional options at this stage would include underpinning, with a major excavation under the existing building, or retrofitting piles.
“Both of these solutions would have taken much longer than ours, and excavating would come with health and safety risks, while getting a piling rig in may have been a challenge,” says Bromley.
Uretek reviewed site investigation data and established the depths under each wall, at which the soil displayed competency in relation to the proposed loading conditions. A geo-polymer was then specified, based on multiple factors such as compressive strength and expansive force
As described in the publicly available paper, the Uretek Ground Improvement method involves drilling a hole of maximum 50mm diameter to the required depth. An injection tube is inserted into the hole and the specified geo-polymer is pumped through a truck-mounted hose into the tube at a precise rate.
Uretek’s geo-polymers are formed from multiple components that, when combined during the installation process, initiate the process of polymerisation. This causes the material to change state from liquid to solid and expand.
“We are very accurate in the locations in which we drill, so we target the relevant areas of soil,” says engineering manager Daniel Hadfield. “The expansion of the geo-polymer improves the soil via compaction or consolidation; it does not act as a new structural body it allows the soil to transfer the required load.”
The mechanical strength of the geo-polymers has been evaluated by Uretek’s material manufacturers using compressive strength tests conforming with European standard EN826.
As well as the detailed, accurate calculations carried out by Uretek engineers ahead of specifying a solution, the effectiveness of the injections can be proved with a physical site check.
Throughout the geo-polymer injection process, relevant parts of the overlying structure are monitored using rotary lasers and mounted sensors placed close to the active injection point.
Each injection continues until a reaction of less than half a millimetre is registered, indicating the treated soil has been reinforced sufficiently to carry the load of the structure, as the upward force is acting upon the underside of the above foundation.
A final check is carried out to quantify the increase in soil strength. Dynamic cone penetrometer testing is carried out using penetrometers with 30kg falling weights. A measurable indication of strength can be gained by measuring how many “blows” are required to drive a rod 100mm into the soil which is being tested.
Outdating traditional methods
The firm believes its method is making traditional excavation and piling solutions look increasingly dated, and offering engineers a safe, time-efficient, minimum-disruption alternative.
On the National Gallery of Ireland project, the geo-polymer was required up to a depth of 2.5m for an overall length of 28m. “It was successfully injected within three days and we were off site allowing the contractor to get on with the job,” says Hadfield. “Using other methods, main works might have had to stop for weeks and weeks.”
Uretek is increasingly being involved preemptively on construction projects, as well as picking up its traditional reactive works when something has gone wrong and ground needs stabilising fast.
“We are involved a lot more at design stage,” says Hadfield. “If people are looking to add to buildings, and they have got incompetent soils, they now are beginning to understand there is a quick, effective way of strengthening it.”
The firm works on roads, in the rail sector, on airports, and in the commercial sector as well as on a range of other buildings.
Programme saving and lack of disruption
“The biggest plus-points are the programme saving, and the lack of disruption. We give clients much less of a headache than other methods” says Bromley.
Uretek has worked on major motorway schemes, as well as smaller roads. At Northumberland Avenue in Reading, Berkshire, years of damage to a concrete slab and increased heavy vehicle use had led to surface fretting and potholes.
A survey showed that the integrity of concrete slabs was being compromised by weak ground along a 400m stretch of road. Uretek drilled through the road and subsurface and injected its Geo-polymer resin at depths of up to 3m.
In the rail sector, Uretek worked on a project in Farnham, Surrey, to stop settlement in base slabs at a rail depot from disrupting train services. The firm injected its resin into a large area over five weeks and stabilised 6,000m2 of slabs with minimal disruption to operation of the depot.
“There is a common problem on the railways called wet bed, where water comes up under the rails,” says Hadfield.
“We drill through the slab and inject a geo-polymer that displaces water and creates an impenetrable barrier to stabilise the soil under the slabs.
“This is an area we’re hoping to work in more.”
Uretek has carried out in excess of 200,000 geo-polymer injection projects over 37 years. Its geo-polymers work on most soils, including granular, cohesive, organic and made ground.
The material Uretek uses has a design life in excess of 100 years and has been tested to remain stable for at least 60 years at a wide temperature range. It is inert and can be treated as building material waste if ever excavated.
“It is such a versatile solution and we believe it is the future of ground engineering,” says Hadfield.
In association with Uretek