The geotechnical properties of some till deposits occurring along the coastal areas of eastern England

Abstract

Deposits of till are found along the coastal areas of eastern England from Northumberland to East Anglia. The geotechnical properties of tills from three areas, namely, north Norfolk, Holderness and Teesside have been investigated. The dominant clay minerals in the fine fraction of the tills are kaolinite and illite. As would be expected, quartz is the other dominant mineral in the fine fraction of the tills. Deposits of till occur in the Anglian and Devensian stages of the Quaternary succession in Norfolk. All these tills are matrix-dominated, with clay generally forming less than a third of the matrix. They are either firm or stiff with low or intermediate plasticity and have relatively low values of shear strength. The tills are either inactive or have normal activity and all have low sensitivity. Their consolidation properties are characteristic of stiff clays. The glacial deposits of Holderness consist primarily of tills. Except for the oldest of these tills, which is Wolstonian, the others are of Devensian age. The fine fraction usually constitutes up to 60–80% of the deposits. These clays have a low plasticity. The tills of Holderness have a low sensitivity and a relatively low unconfined shear strength. Their values of shear strength are reduced from peak values, to residual values primarily by a reduction in the cohesion parameter. Like the tills from the other two areas, the pore water pressures on testing in, consolidated, undrained conditions rose rapidly to a peak which was followed by a gradual falling off as failure was approached. The glacial deposits of the Teesside area are of Late Devensian age. These lodgement tills were products of successive ice sheets. The tills are thickest in the north and west of the area, and are characteristically unsorted and matrix dominated. They are of low to intermediate plasticity, and vary in consistency from firm to hard, generally being stiff to very stiff. The results of triaxial tests indicate a reasonably wide range of strength.