A survey of some geotechnical properties of the Tees Laminated Clay of central Middlesbrough, North East England

Abstract

The Tees Laminated Clay was deposited in a proglacial lake which occupied the Teesside area during late Devensian times, disappearing about 13 000 y ago. The laminations consist of alternating thin layers of clay and silt, and represent seasonal increments of sediment. Fissuring is common in the upper few metres of the laminated clays, which reach a maximum thickness in parts of central Middlesbrough of just over 9 m. Illite and kaolinite, with lesser amounts of chlorite, dominate the mineral composition. Quartz tends to account for less than 30%. The notable carbonate content may be diagenetic in origin. The birefringence ratio of the clay minerals indicates a medium degree of particle orientation which suggests a partially flocculated fabric. These laminated clays have a high plasticity. However, the liquid and plastic limits of the silty layers differ significantly from those of the clay layers or the bulk samples. The clay fraction has a greater influence on these limits than the silty fraction. In addition, the linear shrinkage, liquidity indices and consistency indices of the silty layers differ appreciably from those of the clay layers and the bulk samples. The clays are inactive. The orientation of the laminations in relation to the direction of maximum principal stress influences the shear strength, the lowest strengths being developed when these orientations are between 30° and 60°. The stress paths, anisotropic ratios and values of A f indicate that the Tees Laminated Clay is normally consolidated or lightly overconsolidated. The McLamore-Gray concept possibly can be applied to the anisotropic strength behaviour.