ABSTRACT
The British land mass was better defined in Oligocene and later times and became a source of muddy detritus for surrounding areas. The geological evolution of Great Britain has contrived to leave a considerable surface area underlain by overconsolidated clay soils. The most marked difference in origin within the overconsolidated clay group is perhaps that between the marine, dark-coloured mudrocks of Mesozoic and Cenozoic age, and the glacially-overconsolidated pebbly clays deposited by Quaternary glaciers. Liquidity index is a measure of the consistency of a clay soil, since it relates the in situ moisture content to the plasticity parameters. The increase in drained brittleness can be ascribed to a greater propensity for alignment of grains along a shear surface in the soils enriched by clay minerals. Significant changes in the physical properties of marine overconsolidated clays are caused by chemical weathering.
