Specialist contractor Uretek has been stabilising the ground quickly, safely and with minimum disruption for 25 years in the UK. It is now experiencing its most exciting growth period as more projects and sectors benefit from its patented geopolymer injection solution.
When subsidence caused large cracks to appear in houses on the Cleeves Road estate in Glasgow, many of its elderly residents were adamant that they would remain in their homes while repair work was carried out. Not only did they stay, but they were able to sit in their living rooms and watch TV while technicians from specialist ground improvement contractor Uretek worked around them, injecting geopolymer resin into the ground from within their homes.
The Cleeves Road project (outlined in more detail on page 22) goes some way towards explaining why Uretek’s method for stabilising the ground has grown in popularity over the past 25 years, since the Finnish-based company first licensed the product for use in the UK.
The technique was originally invented as a ground improvement solution for subsidence problems caused by the cycle of freezing and thawing that weakened the ground in northern Europe. Since then, many more projects have benefited from geopolymer injection, a treatment that fills microscopic voids in the ground to consolidate and compact it.
The geopolymer ground improvement technique is clean and non-disruptive - it requires no prior excavation or disposal of spoil, no cumbersome concrete lorries requiring access, nor any messy cementitious grout to do the job.
“Geopolymer injection is very different to cementitious grouting, which relies on hydraulic pressure to work,” explains Uretek managing director Roland Caldbeck.
“Geopolymer injection improves the ground by using the pressure generated from the chemical reaction of the geopolymer mix. The process involves filling microvoids in the ground, and consolidating and compacting the soil. When you achieve compaction, you achieve slab-lift. All the compounds in the resin are used up in the reaction and the end product is inert.”
Caldbeck adds that for cohesive soils, flooding the pores with the geopolymer increases the bearing capacity of the ground. Where soil is more granular, geopolymer injection has a consolidating effect. The injected geopolymer resin has an almost immediate stabilising effect
on the ground - typically taking 15 minutes to harden - so the process is also quick.
Geopolymer injection requires very little equipment, so mobilisation and demobilisation is discreet and speedy As the process often involves fewer truck journeys compared with underpinning and other grouting techniques, it is often a lower carbon footprint option too.
Now having been used in more than 50 countries and 100,000 projects worldwide, engineers working on large airports and highways projects are turning to Uretek as the first port of call for solving subsidence problems.
“Often the cost of fixing a problem in the ground is minimal compared with the cost of disruption caused by a road, railway or airport being out of action. Our solution is so much faster than most others and is also long-lasting,” Caldbeck says.
Case studies on the following pages demonstrate the range of projects undertaken by Uretek in the UK, all providing speedy permanent solutions with minimum disruption.
The geopolymer mix can also be adapted to suit mass void-filling or, to treat the weakest ground conditions where ground improvement is not an option, a piling solution can be created by constraining the geopolymer within a geotextile sack in the ground.
“We have a niche product which has a wide range of uses,” comments Caldbeck. “The UK market has grown from being predominantly based in the residential sector to being equally split between residential, commercial and infrastructure projects. We have completed more than 10,000 projects in the UK alone.”
For many of the projects, safety has been a big factor in the Uretek solution being chosen. Subsidence inevitably leads to weaknesses in the superstructure, and in those situations, invasive ground improvement techniques could lead to collapse. And since the process requires no excavation or infilling, there are also fewer on-site safety risks.
Depending on ground conditions and the degree of treatment required, there are more than 30 different polymer mixes which can be prescribed to cure subsidence or other ground-related issues. “We can even create bespoke mixes to achieve specific expansion ratios and different compressive strengths,” explains Caldbeck. “This controls how far the resin will flow before it starts to harden - it’s all very fast, we’re talking five or 50 seconds curing time,” he adds.
As the current workload suggests, consulting engineers working on challenging infrastructure projects are turning to Uretek for ground improvement solutions. Its own engineering team has also recently expanded as the company takes on more design responsibility to meet demand.
“We are integrating more and more with the engineering community, providing solutions at feasibility stage,” says Caldbeck.
Pre-treatment ground testing carried out by Uretek identifies ground conditions outlined in site investigations and pinpoints where and to what degree ground improvement is required. Where required, Uretek also carries out post-treatment ground testing as a final check to demonstrate that the work has been successful.
Caldbeck predicts the next 25 years will see Uretek’s geopolymer solution take on a wider range of projects, probably with ever more challenging constraints.
“Even when a site is difficult to reach, where work has to be coordinated around very specific scheduling or must be sympathetic to environmental or historic features, we can treat the ground and maintain ‘business as usual’ for commuters, workers, residents and shoppers,” he says.
A 1960s housing estate in Glasgow built on an infilled limestone quarry started experiencing subsidence problems after a water main running through the area burst.
About 38 of the 300 properties on the Cleeves Road estate exhibited cracks in excess of 15mm, requiring immediate action.
A solution to stabilise the ground with minimum disruption was required so that residents did not have to be rehoused while repair work took place.
Uretek was appointed to inject its patented geopolymer resin into the shallow soils beneath the homes to fill voids and consolidate the ground. Two different resin mixes were prescribed for the ground conditions, based on earlier trials.
Uretek’s clean and quick solution was favoured over conventional cementitious grouting- particularly as work had to take place inside homes. Uretek liaised closely with residents to explain the procedure and to work around them.
Remediation took just 16 weeks and involved treating the ground to a depth of 4m beneath 900 linear metres of internal and external walls.
The concrete base slab of a 60-year-old railway maintenance shed at Farnham, Surrey, had begun to settle due to the increased weight of modern rolling stock, drainage Project Farnham rail depot Client Network Rail Main Contractor Osborne Rail Services Consultant Frankham Consultancy and washout problems, crushing of loose material and long-term consolidation of clay layers in the ground.
Work to stabilise the ground had to be undertaken quickly and without significant disruption to the facility’s operations, as well as to the adjacent railway.
Although speed restrictions were applied to locomotives which passed through the depot, there was a significant risk of derailment due to the weak and uneven ground beneath the slab and track.
Neither conventional piling nor replacement of the 6,000m2 slab were viable options due to the short time available to carry out the work.
Uretek’s solution was to inject geopolymer resin, which achieves 90% of its strength within 15 minutes of application. Using a highly controllable method of injection,
the resin filled voids in the ground and lifted the slab within tolerances of +/- 10mm over 10m2 to ensure that within five weeks, repair work was complete.
The slipway at Peterhead Port, on the north-east coast of Scotland, was built in 1931 and designed for fishing vessels, which were longer, narrower and considerably lighter than those in use today.
While dock machinery had been upgraded to cope with the increased size of ships, civil engineering infrastructure had not and settlement of up to 80mm had been detected on the concrete slipway.
The option of building a thicker and more heavily reinforced concrete slab over the whole area and reinstating the rails was considered, but would have been too disruptive to port operations and to marine wildlife. This solution may also have required the existing concrete slipway to be broken up and removed, which would have added to costs.
Instead, Uretek was appointed to provide a solution that would be non-intrusive and could be completed much more quickly. Over two weeks, it injected geopolymer resin up to 10m beneath the ground to strengthen it and lift the slipway to required levels and tolerances. Geopolymer resin was injected every 1m below 97 linear metres of concrete slipway, without disrupting port operations. The rails were then repositioned on the renewed slipway.
When the concrete road slabs on the main approach to Southampton Port began to show signs of excessive movement, Southampton City Council was keen for repair work to be carried out quickly and without having to close the road.
As around 1,500 lorries use Millbrook Roundabout at the junction of the A33 and A35 every 24 hours, the solution had to keep traffic flowing. A “rocking” movement in the road slab had been detected, but replacing it would have meant a minimum eight to 11 month road closure.
Uretek’s solution was to stabilise the ground under the road using its injectable geopolymer resin. Around 8,500m2 of slab was stabilised, using 380 injection points at 1.5m centres, to a depth of 2m.
Work was carried out outside the morning and evening peak traffic periods using only a truck, hose, laser level and a drill, allowing for a quick and clean turnaround ahead of rush-hour.
Uretek’s discreet work was completed in just five weeks, without the inconvenience, cost and environmental damage excavations, disposing of arisings and causing traffic congestion.
Originally built in the 14th century, Scaleby Castle in Cumbria started to show signs of significant movement as stonework had begun to rotate outwards and away from its 16th and 19th century additions. Being both a Grade I listed building and a Scheduled Ancient Monument, owner Lord Henley sought a permanent solution that would not harm the building.
A site investigation revealed that a saturated sand layer beneath the castle walls was the primary cause of the problem and that immediate underpinning or ground improvement was required to save the tower from eventual collapse. A solution which involved any degree of excavation was considered too risky, given the age of the building.
Over two days, Uretek technicians drilled small diameter boreholes 2-3m deep beneath the castle walls and from within the internal courtyard. Geopolymer resin was then injected through the boreholes to strengthen the ground and prevent further settlement. The polymer naturally filled areas of weakness in the ground and, as it hardened and expanded, exerted dynamic forces of up to 250t/m2 to increase the ground’s bearing strength.
Road slabs on two of the main routes into Bath city centre showed signs of movement and had to be stabilised without causing traffic problems or affecting residents and businesses. Uretek worked closely with Bath and North East Somerset Council and stakeholders to achieve a suitable working schedule to stabilise sections of North Parade and Manvers Street.
The result was that, instead of working 24 separate shifts across days and nights, residents and business owners expressed preference for the work to be carried out during shorter night-time only periods.
A near zero-disruption programme was developed whereby four geopolymer grout injection teams worked across four nights at each location. Borehole drilling only took place between 7pm and 11pm and work was sequenced to allow the roads to be fully open by 6am each morning.
Geopolymer injection treated 1,304m2 of North Parade and 1,150m2 of Manvers Street without disruption to businesses, residents or traffic
flow. Uretek also undertook surveys before and after ground strengthening to verify that the treatment had been effective.
After a series of dry summers and wet winters, the ground beneath the east end of St Mary’s Church in Doverdale, Worcestershire, had settled, causing the stone gable end wall to rotate on its foundation and move up to 30mm.
The church, which is recorded in the Domesday Book and was rebuilt in the early 1800s, was built on shallow foundations of sandstone blocks, over made ground and interbedded sand and gravel and weathered Mercia Mudstone to a depth of 3.7m.
Traditional piling or underpinning was ruled out since they would have required temporary removal of three large tombs just 300mm from the wall.
Ground treatment by geopolymer injection was the most non-disruptive form of remediation. A geopolymer mix suitable to the specific needs of the ground and sensitive to those of the church was selected by Uretek and approved by English Heritage.
Initial work involved geopolymer injection to stabilise vulnerable parts of the structure, before injecting into the ground via 16mm holes drilled at 1.2m centres along the gable wall.
Treatment of 16 linear metres along the gable end and down to the Mudstone level at 3.7m was also supervised by English Heritage.
When the ground beneath the concrete floor slabs of two large “high bay” warehouses in Cheshire began to settle, owner North West Farmers was faced with the prospect of losing half the storage areas of each warehouse for up to four months while repairs took place. As a safety precaution, the use of moveable storage racks had already been stopped across areas of uneven and unstable ground, affecting the facility’s productivity.
Faced with the considerable loss of earnings from reduced capacity, as well as the cost to replace the slab and embedded rails to support the racks, North West Farmers needed a much less disruptive solution.
Uretek’s answer was to stabilise the ground using geopolymer injection, which allowed work to be carried out in small areas at a time, so that the majority of the warehouse could operate as normal. The procedure took just 40 days to complete. The highly controlled technique ensured that the slab lift required to reinstate level working was achieved to within 1mm accuracy.