Partially saturated tailings sand below the phreatic surface

An opportunity to re–examine the liquefaction potential of hydraulically placed tailings sand has been provided by the Canadian Liquefaction Experiment (CANLEX). As part of this experiment, undisturbed samples of tailings sand were recovered after freezing the tailings in situ. Examination of undisturbed cores of frozen tailings sand clearly showed that the specimens were not fully saturated. This was confirmed by both physical measurements and laboratory tests in which gas was recovered from thawing specimens and analysed by gas chromatography. The gas was mainly air although a small amount of microbial gas was also present. Cryogenic scanning electron microscopy and confocal laser scanning microscopy were used to further confirm the existence of occluded gas bubbles. Triaxial undrained compression tests were carried out on undisturbed tailings specimens that were not back–saturated prior to shearing, in order to preserve the in–situ degree of saturation. Occluded air bubbles within the tailings sand, ev...