Morphology, Ageing and Engineering Behavior of Sands

This paper reviews approaches to quantify grain morphology and microfabric and their influence on engineering behavior of sands. Grain morphology and microfabric induced by ageing are quantified in terms of simple indices which are shown to be correlated with mechanical characteristics of sands. It is stressed that correlations based on SPT/SCPT values developed for a particular type of sand cannot be extrapolated for all types of granular materials. Cyclicpre-straining and secondary compressionmechanisms of ageing of sands are shown to give identical results. Strain-time response of a sand, that has experienced increased vertical strain under an effective stress level either by secondary compression or cyclic prestraining, is shown to give an excellent demonstration of the influence of grain morphology and constancy of Ca C,. Based on analysis of available data for uncemented aged sands, it is shown that majority of improved behavior of aged sands is primarily due to particle interlocking planar type contacts and that during ageing the changes in grain contact types, from tangential to planar, occur at practically constant volume. Field studies of aged sands and quantitative evaluation of their microfabric are recommended for better understanding of the mechanisms of ageing and their effect on mechanical characteristics of aged sands.