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Effects of aging duration, stress ratio during aging and stress path on stress-strain behaviour of loose Fraser River sand Lam, Chun Kit Keith

Abstract

Recent studies on aging of sands mainly emphasize the effects of aging duration on creep deformation and soil stiffness. Factors such as stress ratio, stress path and confining stress have not been investigated extensively. This research was conducted to investigate the effects of aging duration, stress ratio during aging and stress path on the stress-strain behaviour o f loose Fraser River sand. The main objective of the work was to extend a previous study (Shozen, 2001) to longer aging times and to a greater range of stress paths and stress ratios. Loose reconstituted samples with relative densities (D[sub r]) of approximately 20% were consolidated at stress ratios of 1.0, 2.1 and 2.5 and aged from 100 to 10,000 minutes prior to shear testing along four different stress paths. Test results showed that age stiffening effects were observable at the beginning of shearing regardless of the stress conditions applied to the samples. The effects were more pronounced at higher stress ratios and for older samples. The overall stress-strain behaviour was unaffected by aging. The magnitude of the increase in secant stiffness was greater as the strain increment decreased. Test data also indicated that for strains smaller than 0.2%, aged samples with D[sub r] of 20% had the same or greater stiffness than unaged samples with D[sub r] of 50%. Results from this study suggest that for loose Fraser River sand, the stiffness at very small strains ( G₀ or G[sub max]) may be more sensitive to age than previously thought. The observations imply that for laboratory testing or physical model testing, repeatability of test results will be improved by a consistent approach to aging of samples. For interpretation of in situ tests, the age of the deposit should be carefully considered to enable the estimation of representative engineering properties of the soil.

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