Solution Feature Investigation and Assessment
The dissolution of soluble rocks, including limestone, gypsum and chalk, can result in subsurface voids, commonly referred to as a ‘sinkhole’, which might affect foundations and other infrastructure.
A desk-based soluble rock risk assessment, in accordance with Edmonds (2001) and/ or CIRIA C574, is often initially carried out, particularly prior to new development.
Solution Feature Investigation, Brixham
A solution feature investigation and assessment was undertaken by Ruddlesden geotechnical at the site of a proposed residential development in Brixham.
The consulting engineer had recommended Ruddlesden, having prior experience with solution features (caves) beneath another residential development site within the area.
Based on the findings of the Phase 1 geotechnical assessment, the site was considered to be at high risk of being underlain by solution features that could affect the proposed development.
A geotechnical investigation, comprising a combination of open-hole rotary ‘probes’ and cored boreholes, was undertaken. The boreholes were targeted on the corners of the proposed plots.
The investigation indicated that one of the plots was underlain by a substantial cave (up to 5m high), at a depth of less than 10m below existing ground level. The cave appeared to be filled with sediment and the overlying rock had dilated and partially collapsed into the cave as a result of its presence.
Nevertheless, following a detailed assessment of the ground conditions encountered, it was considered that there was a sufficient thickness of competent limestone present to bridge the cave and that a reinforced concrete ground beam would be able to support the proposed property (even in the event of ground subsidence) and that there was no requirement for infilling of the solution feature or piling the foundations to competent rock beneath the cave.