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New technique to speed subsidence work


GROUND IMPROVEMENT contractor Uretek claimed last month that a newly developed deep resin injection technique can cut the time taken to rectify subsidence by as much as six times.

Uretek is already using its new Power Pile system on its first UK contract - a domestic subsidence insurance claim job in West Lancashire. It has two additional contracts lined up to start in the new year, said managing director, Chris Davies.

Power Piles are resin-filled geotextile bags made from a densely woven high strength polypropylene. The bags and injection rods are installed into boreholes of 63mm to 100mm diameter. As resin is injected, the bags inflate displacing the surrounding ground until resin injection pressure and earth pressure are in equlibrium.

'This is a very quick technique.

Underpinning work done by our parent firm in Denmark indicates that 30 to 50 linear metres of Power Piles can be installed in a week.

It would take up to six weeks to achieve the same result using underpinning, ' claimed Davies.

He said evidence so far was that the technique was 'significantly cheaper as well as faster' than underpinning or mini-piling.

As resin is injected, the Power Piles displace and compact surrounding ground, making them ideal for soft clay, peat, and other types of loose material, Davies added.

'Displacement and compaction of the surrounding ground creates huge skin friction. The more piles you put in, and the closer the centres, the higher that friction gets, ' he said.

Installation is typically at 1m to 1.5m centres, with piles 'inflated' to diameters of 350mm to 750mm.

Davies believes there is potential to increase this width to 1.5m.

He said recently completed tests in Denmark showed end bearing capacity of 1000kPa to 2000kPa.

Depths of over 7m can be achieved by installing multiple geotextile bags down deeper boreholes, Davies said.

Uretek's established injection technique creates rafts of polymer resin. It is typically used to stabilise subsiding walls and slab structures.

Expansive resins can be used for restoration close to original levels.

Using geotextile bags to contain the resin enables a far higher degree of control over placement of the resin forming the new foundation.

Uretek is now developing designs combining its Power Pile and raft injection techniques to improve bearing strength further still, Davies said.

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