Static Fatigue Produces Time Effects in Granular Materials

Time effects observed in tests on sand with different constant strain rates as well as creep tests and stress relaxation tests initiated at different stress levels exhibit patterns different from those observed in clays. It appears that time effects in sand may be associated with crushing of particles, and single particle crushing has therefore been studied. A mechanistic picture of deformation and time effects in granular materials is presented in which the time effects depend on interparticle friction, grain crushing and grain rearrangement. The phenomenon of static fatigue of individual particles appears to be at the root of time effects in sand. A review of previous studies of static fatigue is presented. Load-controlled tests on individual sand particles in the form of spherical glass beads (quartz) were performed by maintaining constant loads lower than the short term crushing loads. As do rock specimens in triaxial compression, the glass beads show effects of time to crushing.