Fabrication of Silty Sand Specimens for Large- and Small-Scale Tests

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Courtesy of ASTM International

In the course of research concerning the relation of cone penetration results and liquefaction resistance, it was necessary to develop a reliable method for preparation of silty sand specimens for laboratory triaxial testing (3.6 by 7.1 cm in diameter) and for a large-scale calibration chamber (1.5 by 1.5 m in diameter). The objective was to simulate the in situ soil fabric and to allow for creation of a range of densities. Four alternate procedures were studied, including kneading compaction, pluviation through air, pluviation through vacuum, and consolidation from a slurry. The primary conclusions from the research were:

1. Kneading compaction is effective in producing laboratory specimens with a range of densities, but it is not an effective procedure for placing these materials in the large-scale calibration chamber.

2. Pluviation through air and vacuum creates specimens with unrealistically high void ratios. Obtaining a range of densities was not possible.

3. Slurry consolidation proved to be successful in creating specimens with a range of densities and was the technique chosen for the calibration chamber.

Only vertical drainage was used in the calibration chamber to avoid formation of a specimen with a soft core surrounded by stiff sides. Eighteen to twenty days were required for consolidation, and the density of the specimens along a vertical profile varied by no more than 6% from the average density. There was little evidence of segregation of fines.

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