Comparison of factors influencing time-dependent strength gain in recently disturbed sand deposits

The study presented here investigates factors causing time-dependent strength gain in recently disturbed granular materials, a phenomenon commonly referred to as "sand aging." Sand aging has been recorded following earthquakes, deposition of fill, and soil improvement projects. Its manifestation includes an increase in cone penetration test (CPT) tip resistance (q_c|N), standard penetration test (SPT) blow count (N), and small strain shear wave velocity (V_s) with time. While there is still no consensus on the dominant mechanism, several hypotheses have been proposed for the causative mechanism. These include a chemical mechanism (i.e., precipitation of a cementing agent); a mechanical mechanism (i.e., asperity shearing and particle rotation); and dissolution of air bubbles. Because of the expanding database of sand-aging case histories, it is now possible to compare recorded aging effects to the proposed mechanisms influencing sand aging. Toward this end, data from 26 case histories, including three field-scale experiments conducted by the authors at two different sites, were used to investigate the magnitude of sand aging as a function of the factors hypothesized to be responsible for the aging. From this study, disturbance method, pore fluid composition, mean grain size, q_c1Nfresh (as a proxy for D _r), and σ_v were found to influence aging, while the influence of the soil's chemical composition, temperature, coefficient of uniformity, grain shape, and aeration of the pore fluid were inconclusive.