Stable future for exeter's past

Settlement – possibly aggravated by global warming over the past century – has for many years posed a problem for Victorian buildings at Exeter's Royal Albert Memorial Museum.

The two main museum buildings have been slowly leaning into a backfilled Norman ditch running under part of the structure, with differential settlement creating cracking, distortion and rotation of the masonry wall panels. The problem was resolved last month without major disruption to the sensitive archaeological site.

"In an effort to halt the settlement and prevent further damage to the historic fabric, we wanted to stabilise the foundations," says Stephen Beggs, civil and structural engineering director at consultant BDP.

"Rather than use traditional underpinning, which would have created new localised stiff points in the ground and required large scale excavation, resin injection was considered to be a more sensitive solution. There was also an archaeological benefit to minimising disruption to the ancient soils."

BDP worked with Uretek UK to develop plans for injecting under several lengths of the wall. Over three weeks, Uretek used its Deep Injection process to 95 linear metres of wall. This involves injecting expanding polymer resins through small diameter holes immediately underneath the foundations and then at greater depths to fill voids and consolidate the ground. Only 10% of the weight of concrete, the resins do not add significant stress to the surrounding ground, yet provide compressive strength under load of up to 10,000kPa.

For additional strengthening Uretek also applied its new PowerPile system to another 56 linear metres. This involves injecting expanding resins into specialised geotextile tubes, which concentrates the resins in a highly compact area and compresses the ground in between. Average injection depth was 3m.

"The works were completed with minimum intrusion to the fabric of the building. We expect the resin to stabilise the foundations and result in negligible further movement," says Beggs.