Renovating the Old Infirmary at Stonyhurst College in Lancashire this spring required a fast, non-intrusive method of ground improvement.
The Grade I listed buildings are up to 400 years old. Indeed, Oliver Cromwell is reputed to have slept on a table there the night before the Battle of Preston in 1648. Over many years, gradual settlement of the central core of the Old Infirmary has taken place, mostly due to leakage from stone drains.
'We needed to make sure of level access, and there was no point in levelling the floor without curing the problem, ' explains Brian Edmondson, technical director of consulting engineer TD Bingham.
Conventional solutions such as piling were ruled out because of restricted access in the basement, and also the time factor. 'Pinning through a wall and then piling on either side is very simple to do on drawings, but it's sometimes very difficult in practice, especially with all the drains down there, ' says Edmondson. 'It could have taken six months.' Having used Uretek processes before in the Isle of Man, he recommended resin injection.
Where ground conditions are suitable, resin injection has the advantage of minimal disruption; no excavations are needed, and there is little or no dust or mess.
Uretek's methods are fast to apply, and restricted access is usually no problem, as only a hose needs to be brought to the application point, with the rest of the equipment staying on the truck.
Over the past 25 years, Uretek has pioneered and developed two main processes for resin injection: the floorlifting method, which fills voids and relevels sunken flooring, and the deep injection method, which provides an alternative to piling and underpinning when dealing with subsidence. Different applications demand varying degrees of expansive force, and the resins are selected on a case by case basis to produce the optimum results.
The most powerful resin available is Geoplus, with an expansive force of up to 10,000kPa - 20 times that of other polymers. Geoplus is used for deep injection work, and has the added advantage that it does not add significant weight to the surrounding ground.
While the resin is injected the compaction effect is verified in real time using a laser level placed on the floor or wall, which monitors lift. No overlift occurs because the set-off time of the material is almost instantaneous.
At Stonyhurst, two teams from Uretek spent a total of 14 days injecting resin at 1m intervals to a depth of 5m under the load bearing walls in the Infirmary basement, filling voids and consolidating the brick fill and sandy clay.
The desired ground improvement was achieved, enabling alterations to the building to proceed without delay.
'We are very pleased with the work, ' says Michael Hartley of Cassidy & Ashton, architect for the renovation projects.
'The Uretek treatment has allowed reconstruction work on the Old Infirmary to proceed on schedule.' www. uretek. co. uk