

Observations of time effects in triaxial compression tests performed on crushed coral sand with constant strain rate, creep tests at different stress levels, and stress relaxation tests initiated at different stress levels are presented. The classic time effects found in most materials, i.e. increasing stiffness and strength with increasing strain rate and corresponding creep and stress relaxation behavior, are not observed in sand. Observations from the experiments show that strain rate effects are negligible for crushed coral sand, unlike for clays in which strain rate effects are significant. Further, the observed stress relaxation behavior was not in “correspondence” with the measured creep behavior. Therefore, the amount of stress relaxation predicted on the basis of model parameters determined from creep experiments is too small. It is concluded that sands do not exhibit viscous effects, and their behavior is indicated as “nonisotach,” while typical behavior of clay is termed “isotach.” Thus, there are significant differences in time-dependent behavior patterns of sands and clays. In another investigation on Antelope Valley sand the measured responses in creep and stress relaxation tests and in constant strain rate tests exhibited similar behavior as the crushed coral sand but with smaller discrepancy between the creep and stress relaxation tests. An explanation for these non-viscous and dissimilar effects for different sands is proposed and relates to the amount of grain crushing that occurs in different sands.