Predicting natural cavities in chalk

Introduction Chalk is a soluble carbonate rock with extensive karst development. Natural cavity occurrence initially appears to be random. In an area where the degree of influence of all cavity formational factors is similar, but dissolution is focused on one set of joints rather than another, then solution feature occurrence is perhaps random. This might be termed the ‘microscale’ view, measured at a scale of metres. However, if the pattern of natural cavity occurrence is considered at a ‘macroscale’ level, say measured in hundreds of metres or kilometres, then spatial patterns emerge suggesting dissolution is not as random as it might first appear. Spatial characteristics of natural cavity occurrence on the Chalk In order to analyse the spatial characteristics of natural cavity occurrence it was first necessary to collect as many records of solution feature occurrence as possible from published and unpublished sources including local authorities, Construction Industry Research and Information Association (CIRIA), Transport Research Laboratory (TRL), Building Research Establishment (BRE), National House Building Council (NHBC), the Environment Agency, water companies, and site investigation reports. Particular emphasis was placed on fieldwork to record new features revealed in a wide range of engineering works, road and motorway construction, and on visits to large numbers of working/disused chalk quarries and aggregate workings. A database of 2226 natural cavities was compiled, composed mainly of solution pipes, sinkholes (dolines) and swallow holes. The spatially related database (each cavity location being recorded by National Grid Reference) was carefully scrutinized to determine