The fabric (that is, the physical structure) of sand, and the effect of aging, play a fundamental role in determining the stresses necessary to trigger liquefaction under earthquake loading. Recent observations indicate that changes in sand fabric, as measured in the field, may result in a rapid initial gain in stiffness due to aging, but that dynamic loads, such as those induced by earthquakes, cause this stiffness to degrade. This results in significant fluctuations of the sand liquefaction resistance with time. It is possible that both physical and chemical mechanisms may contribute to these age-related changes in liquefaction resistance. The basic intent of this research project is to investigate in the laboratory whether beneficial ageing effects on soil fabric can be destroyed by relatively low levels of cyclic strain, thereby simulating the effects of earthquakes which are smaller, but more frequent, than the "design earthquake" for a given site. The goal is to investigate the earthquake- induced reversibility of the effects of time on sand fabric, thereby concluding whether it is a matter of practical concern in evaluating the liquefaction potential of a given site. If this turns out to be the case, it will bring into question the way in which penetrometer-based design methods are currently applied, and will further suggest that a conservative design approach may be to base the liquefaction potential evaluation on the resistance of the sand in a freshly-deposited state in the laboratory.
