FOUNDATION CONTRACTOR Uretek used its deep injection underpinning system to stabilise a 700-year-old listed building in Cumbria.
The tower of Scaleby Castle, built in 1307, has been steadily deteriorating over the past 500 years.
Lord Henley, who owns the country house adjoining the tower, became concerned with the dangerous outward cant of the stonework and sought the advice and assistance of Blackett-Ord, a consulting engineer and specialist in the repair of historic buildings, and Elaine Rigby Architects.
A site investigation revealed that a saturated sand layer beneath the castle walls was the primary cause of the problem. Immediate underpinning was required to save the tower from eventual collapse.
The deep injection method was chosen because restoration had to be carried out without disturbing the archaeology and the technique did not require excavation of the foundations.
Uretek engineers were on site for only two days, drilling strategically placed small diameter boreholes 2-3m deep directly beneath the castle walls around the outer perimeter and in the internal courtyard.
They then injected high density polymer resin, which hardens within 15 seconds to the density of concrete but with only one fifth of its weight.
As the resin is injected it fills any areas of weakness to increase ground strength. As it hardens it expands, exerting dynamic forces of up to 250t/m 2, capable of lifting even a multi-storey building.
During the deep injection process the tower walls moved inward by 1-2mm. Movement was measured by laser sensors and the injections carefully controlled to avoid over-correction.
The main contractor for the project was Historic Property Restoration and the work was supported by a grant from English Heritage.