New Vacuum-Preloading Technique for Ultrasoft-Soil Foundations Using Model Tests

Abstract

The effectiveness of vacuum preloading is a very important aspect of the improvement effect of dredger fill. This study experimentally investigated this issue using four different vacuum-preloading methods with a physical model test. The ultrasoft soil was obtained from Tianjin, China, and the samples were prepared in a slurry state using a physical model testing device. The samples were subjected to the traditional vacuum-preloading method and three modified vacuum-preloading methods (multistaged vacuum preloading, vacuum preloading with intermittent ventilation, and vacuum preloading with air injection and intermittent ventilation), in which the water discharge amount, rate of water discharge, amount of settlement, and pore-water pressure were analyzed as well. The results indicate that, under the vacuum preloading with air injection and intermittent ventilation mode, the water discharge amount increased faster, and the final discharge volume was greater than that obtained under the other methods. Meanwhile, the variation trend characterizing the settlement was similar to that of the water discharge amount, where the relative settlement under the vacuum preloading with air injection and intermittent ventilation mode was approximately 1.8 times that under the traditional vacuum-preloading method for the Tianjin hydraulic fill foundation. In addition, the results for the water content and dry density indicated that the vacuum-preloading method with air injection and intermittent ventilation was more effective than the other vacuum-preloading methods in terms of improvement in the Tianjin, China, area.