Mechanism of air-boosting and its effects on vacuum consolidation

This study aimed to address some basic issues about an air-boosting vacuum consolidation. Through theoretical analysis, it has been clarified that air-boosting pressure is not a consolidation pressure, and the efforts for developing a consolidation theory considering the effect of air-boosting pressure are unnecessary ones. Air-boosting can cause pneumatic fracturing in a soil mass, and equations for estimating the minimum air pressure required have been newly derived based on cavity expansion theories. Then, effects of air-boosting on a vacuum consolidation have been identified as: de-structuring, dewatering, and mitigating apparent clogging around drains. Then, by analyzing some published data of laboratory model tests using clay slurries, it is shown that mitigating apparent clogging contributed to about 30%–60% of the effect of air-boosting (increase settlement), and other part could be the effect of dewatering. Increase air pressure and duration of air-boosting had positive effects on both mitigating apparent clogging and dewatering, but might be more effect on dewatering.