An assessment of the earth pressure coefficient in overconsolidated clays

The determination of the earth pressure coefficient K₀ in a natural clay deposit is a problem of considerable significance in geotechnical engineering. While the methods for evaluation of K₀ are reliable for normally consolidated soils, significant difficulties still exist in evaluating K₀ in overconsolidated clays, given that it is influenced by the stress history of the material, together with the age, structure, mineralogical composition and depositional environment. Indeed, some of these factors are responsible for the soil becoming anisotropic. The existing framework for prediction of K₀ in overconsolidated soils does not account for any influences caused by anisotropy. The work reported in this paper evaluates the validity of a revised relationship between K_0oc and OCR (overconsolidation ratio) using data obtained from laboratory investigations. The tests were performed on reconstituted and undisturbed samples of Belfast Upper Boulder Clay, London Clay and Gault Clay. Tests were also performed on reconstituted samples of kaolin. The values of K_0oc were determined using various approaches, including on-sample measurements. The results have confirmed that reliable predictions of K_0oc can be made using the proposed relationship.