Abstract

Partially saturated soils consist of three phases: solid particles, air and water occupying the pore space. Their stress strain behaviour is complex and is influenced by many factors including externally applied stresses, soil type, structure, density and suction arising from surface tension across the air-water interface within the soil. Most notably, suction increases the shear strength, and stiffens the soil skeletal response. Upon wetting, however, this increase in the stiffness of the soil skeleton is lost and may be associated with large and non-reversible volumetric collapse of the soil structure. Partially saturated soils are widely spread and these behavioural characteristics need to be dealt with in many engineering problems including foundations, fills and embankment dams, pavements and airfields as well as natural and made slopes. The engineering of partially saturated soils requires expensive and time consuming site characterisation including soil borings, undisturbed sampling and laboratory testing in an unsaturated state. Performing the versatile and non-disturbing cone penetration test (CPT) could allow less costly and more rapid site characterisation. The evaluation of deformation and shear strength parameters of saturated soils from CPT results has a history going back to 1932, but no correlations currently exist for partially saturated soils, and engineers are left to interpret the CPT results performed in real unsaturated soils, using correlations developed for saturated soils leading to unknown misrepresentations in the estimated soil properties. This talk presents the centrifuge modelling and full scale site experiments that have been performed in order to interpret the results of the CPT in unsaturated/partially saturated soils, and to develop for the first time correlations for in situ characterization of unsaturated/partially saturated soils.