Static Fatigue or Maturing of Contacts in Silica Sand

Silica sands are known to exhibit a time-dependent response to applied loads, particularly after they were disturbed, for example, due to compaction. This behavior was documented by a time-dependent increase in shear wave velocity in sand subjected to sustained loads. The change of material properties with increasing time is often referred to as sand aging. While several hypotheses have been proposed to explain the aging process, none has been generally accepted by the research community. The hypothesis advocated in this paper is that static fatigue at contacts between the grains may be a key factor in time-dependent behavior of silica sand. An apparatus was constructed to load individual sand grains, and the time-dependent deflection under sustained load was monitored. The rate of deflection was found dependent chiefly on the surface texture of the grains (roughness), with rougher surfaces at contacts being more susceptible to larger deflection. The process of static fatigue occurring at the contacts is also referred to in this presentation as contact maturing. The results of grain scale testing in the custom-constructed apparatus are consistent with the hypothesis, which implies that contact maturing is a plausible contributor to aging of silica sand.