THE SPEETON CLAY OF NORTH YORKSHIRE, ENGLAND - AN INVESTIGATION OF ITS GEOTECHNICAL PROPERTIES

The Lower Cretaceous in North Yorkshire is represented by a marine suc cession termed the Speeton Clay. The principal minerals in these clays consist of quartz, mica and clay minerals, although pyrite, glauconit e and siderite are notable in some beds. The proportions of clay miner als change within the Speeton Clay and generally illite becomes more i mportant in the younger horizons. The Speeton Clay is a silty clay whi ch generally has a high plasticity, the latter being influenced by the proportion of clay fraction present. All the clays tested were inacti ve although they would appear to have a potential for expansion. Neith er the plasticity nor the moisture content were affected by depth.In t erms of its undrained shear strength, most of the Speeton Clay could b e regarded as a stiff clay. It was also insensitive with generally a l ow slake-durability index. Its coefficients of volume compressibility were characteristic of overconsolidated and heavily overconsolidated c lays.