Evaluating the Dynamic Properties of the Material Skeleton of Liquefiable Sands At Low Confining Pressures

Abstract eng:
A next-generation, combined resonant column and torsional shear (RCTS) system has been developed to measure the cyclic and dynamic properties of all types of soils with high resolution, increased accuracy, and no complications from system compliance. In this study, the dynamic properties of the material skeleton of liquefiable sands from Christchurch, NZ, were evaluated at low, effective isotropic confining pressures, σ 0 ’ < 60 kPa. Bulk samples of poorly-graded fine sand were collected from one site and were transported to the University of Texas. Specimens were reconstituted in unsaturated, loose and medium-dense states for dynamic testing. The small-strain properties (V S – log σ 0 ’, G max – log σ 0 ’ and D – log σ 0 ’) and the nonlinear properties (G – log γ, G/G max – log γ, and D – log γ) were determined at confining pressures of 14, 28, and 55 kPa. Shear strains in these tests ranged over about 4.5 orders of magnitude (from 10-5 % to 0.2%). The small-strain log V S – log σ 0 ’ relationships are in good agreement with field V S – depth profiles. The expected in-situ G/G max – log γ relationship for saturated sand during earthquake shaking is calculated using G/G max values of unsaturated specimens in the laboratory and pore water pressures measured in the field at corresponding strains.

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