Subsidence Investigation, Exeter

A void was encountered during construction works beneath an existing residential property in Exeter. It was feared that the void might compromise the integrity of the property, as the existing foundations were no longer being supported. Ruddlesden geotechnical were called out on behalf of a consulting engineer to investigate the ground conditions, to assess possible reasons for movement and to provide appropriate remedial recommendations.

The Phase 1 geotechnical assessment indicated that this was likely to be due to a damaged rainwater downpipe, which had resulted in the wash-out of loose fines within made ground, associated with the basement of a historical property, present prior to the construction of the Victorian terrace.

A subsequent geotechnical investigation, which comprised hand-held window samples and dynamic probes within the footprint of the existing building, indicated that the made ground was in the region of 3m thick and was present beneath the central and eastern-half of the building.

Ruddlesden recommended that, to guarantee the serviceability and integrity of the existing building, the foundations be underpinned on to the underlying breccia using cantilevered mini-piles or the made ground be consolidated using a low-mobility grout.