Design and Verification of Blast Densification for Highway Embankments of Liquefiable Sands
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2012-10-26
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Alternative Title:Measuring the effect of occluded gas bubbles on stress-strain response of a loose to;medium sand;
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Edition:Final report.
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Abstract:As part of a larger effort to investigate the effects of blast densification on the properties and
behavior of compacted sand deposits, this study presents a procedure for replicating in the
laboratory the occluded gas bubbles believed to exist in the ground after blasting, and a
preliminary evaluation of the effect of these bubbles on the stress-strain response of loose to
medium samples of a fine sand. The procedure for creating gassy soil specimens relied on the
exsolution of CO2 gas from carbonated water when the applied pressure was reduced. A system
was developed for replacing the pore water in a sand sample with water saturated with CO2.
After replacing the pore water, a given amount of bubbles could be produced in the sample by
lowering the backpressure by a controlled increment. Using this setup, a series of drained and
undrained triaxial compression tests were performed on sand samples with void ratios ranging
from 0.62 to 0.82 and containing varying amounts of gas. It was concluded that the presence of
free gas lowered the effective friction angle of the sand by 1.0 to 1.5 degrees compared to fully
saturated samples at the same void ratio. This effect may explain the reduction in cone
penetration resistance after blasting which is often observed in the field.
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