Contact maturing in silica sand

The time-dependent behavior of silica sand after disturbance is a well-documented phenomenon. Engineering manifestation of this effect is encountered, for example, after in-situ compaction of sands. When compacted with vibratory means (or blasting), sands appear to have an almost unchanged (and often slightly lower) resistance to cone penetration immediately after the disturbance. However, the resistance will increase within weeks and months after the compaction process. A hypothesis is advocated in this paper suggesting that delayed fracturing of micro-morphological features on grain surfaces at contacts is a key contributor to the time-dependent response and aging of silica sand. Grain-scale testing was carried out to gain evidence supporting the hypothesis. The results of testing indicate that contacts subjected to constant loads remain active for weeks. The outcome of this process is termed 'contact maturing'. Preliminary tests are consistent with the hypothesis of contact maturing. Numerical simulations of the contact behavior are also undertaken, and the results are illustrated in the paper.