Geotechnical properties of British estuarine clays: Towards a geological framework

This paper examines the geotechnical architecture of Holocene estuarine clays from differing settings in the UK and proposes a geological framework within which these can be understood. Within this framework we identify as significant the depositional elevation, elevational changes after deposition, organic productivity and local palaeogeography. Relative to the tidal frame, depositional elevation determines the level of geotechnical structure through microfabric and particle packing. This is expressed via the position of the ambient void index relative to the sedimentation and intrinsic compression lines and by the consequent geotechnical properties. Estuarine productivity controls the organic component, which, in conjunction with cation chemistry, modifies plasticity and yield behaviour. The combined geotechnical effect of these geochemical factors is described for any soil by a novel concept we term the synergistic influence surface. We illustrate this framework using data from the Forth and Number estuaries, together with a review of published data from the Severn and Belfast. We consider this framework to be applicable to Holocene estuarine deposits in other glaciated regions.