A large proportion of the southern UK is underlain by stiff clays. Improving their
geotechnical characterisation is important for many current and future infrastructure
projects. This paper presents an integrated study of the complex stiffness behaviour of
four key medium-plasticity, highly overconsolidated strata: the Gault, Kimmeridge,
Oxford and London clays. The latter were deposited between the Jurassic and the
Eocene under broadly similar marine conditions. Coordinated programmes of advanced
static and dynamic laboratory measurements have been undertaken on high quality
samples, concentrating on samples taken from similar depths at inland sites and
including triaxial and hollow cylinder stress path experiments employing highresolution
local strain, multi-axial Bender Element and Resonant Column techniques.
A new approach was employed to interpret the hollow cylinder experiments and the
laboratory measurements are examined in combination with independent field shear
wave data. The clays’ stiffness characteristics are shown to be markedly anisotropic,
pressure dependent and highly non-linear. Synthesis allows key conclusions to be
drawn regarding: the relative reliability of alternative measurement approaches; the
potential spread of stiffness behaviours between the clays; and whether the clays’
varying geological ages and burial depths have any systematic influence on their
stiffness characteristics. The results have important geotechnical engineering
implications.