A national study of natural underground cavities in Great Britain - Datacollection, spatial analysis, planning and engineering significance

A national survey of natural underground cavities in Great Britain has been commissioned by the Department of Environment. A large natural cavity database (in excess of 10,000 records) is being collected and entered into a database held on a PC-based computer system which is linked to a CAD package to enable the information to be presented in plan format. The natural cavity types include not only those developed on soluble carbonate and non-carbonate rocks but also certain non-soluble rocks, as produced by the processes of dissolution, piping, erosion and cambering. Particular attention has been paid to cavities occurring in urban areas and those affecting infrastructure. The study has revealed general patterns of subsidence incidence, mechanisms, triggers and effects on existing and proposed surface development. The interaction of natural cavities with man-made cavities has also been explored. Spatial analysis of the database demonstrates factors influencing the broad geographic distribution of cavities. Areas which are more prone to subsidence over natural cavities pose an increased hazard to existing and new urban and infrastructure development. Such areas require special sub-structure and drainage measure designs or ground treatment. In Great Britain the engineering significance of these problematic ground conditions needs promotion to improve awareness amongst engineers and planners. The national study provides a basic information resource to guide planners and engineers on the circumstances in which consideration of potential land instability is appropriate which should help to reduce future problems and links to government policy guidance. This information forms the basis of a geographic information system.