Strain accumulation in dense sands due to shear stress cycles

This paper investigates the response of granular materials to large numbers of shear stress cycles applied after monotonic loading to various levels of mobilized shear strength. Such stress conditions occur underneath the foundations of structures loaded by non-seismic oscillating forces, e.g. those due to wind and sea waves in tall buildings and offshore structures or induced by vibrating machines. Large numbers of load cycles can induce severe irreversible settlements of foundations and occasionally collapse, even when large safety factors are adopted with respect to bearing capacity in static conditions. Dense Toyoura sand has been used throughout the experimental investigation. Monotonic and cyclic tests have been carried out on specimens loaded in triaxial compression and extension, both in drained and undrained conditions. Specimens have undergone a large number of shear stress cycles and the conditions which cause accumulation of large deformations and even collapse have been analysed. An empirical approach for evaluating the accumulated irreversible strains is also presented.