Small strain stiffness anisotropy of natural sedimentary clays: review and a model

Very small strain stiffness anisotropy of sedimentary clays is investigated. First, a general formulation of transversely isotropic elastic model is summarised, followed by a description of its complete parameter identification using transversal and longitudinal wave velocity measurements. Then, an extensive experimental database from the literature is reviewed. A number of general trends in the anisotropy evolution is identified, based on which a model is developed describing the dependency of the ratio of in-plane and transversal very small strain shear moduli on the stress state and overconsolidation ratio. Subsequently, an empirical relation between the ratios of shear moduli and Young moduli is quantified. The most problematic tends to be the evaluation of Poisson ratios and evolution of stiffness anisotropy under general stress conditions. These issues remain to be investigated experimentally in future work.