Time Effects Relate to Crushing in Sand

Abstract

Based on previously obtained experimental results, a mechanistic picture of time effects in granular materials is presented. Accordingly, time effects are caused by grain crushing, which in turn is time dependent, as indicated by static fatigue of brittle materials. Triaxial compression tests have been performed on Virginia Beach sand at high pressures, where grain crushing is prevalent, to study effects of initial loading strain rates on subsequent amounts of creep and stress relaxation. Grain size distribution curves were determined after each test and the amount of crushing, as characterized by Hardin's breakage factor, is related to the energy input to the triaxial specimens. A pattern emerges that indicates the importance of crushing for the axial and volumetric strains, while rearrangement and frictional sliding between intact grains play much smaller roles in the stress-strain and volume change behaviors of granular materials at high stresses and shear strains. Because particle crushing is a time-dependent phenomenon described as static fatigue or delayed fracture, the close relation between time effects and crushing in granular materials is established.