Laboratory Model for Vacuum-Induced Settlement and Suction Variation in Soft Clay

Abstract

The vacuum preloading method is widely used for improving the stability of soft clay when used as a foundation. The method offers many advantages, including increased consolidation rate and bearing capacity. This study was carried out in a laboratory model to investigate the effect of vacuum pressure on water content and pore-water pressure distribution, and hence, soil settlement. Preliminary tests were performed to identify the soil characteristics. The laboratory model comprises a 58-cm-diameter cylindrical tank equipped with a vacuum pump, a Prefabricated vertical drain (PVD), and settlement plates. The soil was placed inside the tank to a depth of 70 cm. The preloading was applied by a combination of an 80 kPa vacuum pressure and a 20 cm-thick surcharge. During the test, water content and pore-water pressure were measured at five distances from PVD and at three different depths. Results show that the water content varies with both the distance from PVD and depth. On the other hand, the pore- water pressure increased with distance from PVD. Consequently, the soft clay in the cylindrical tank experienced nonuniform settlement. At 130 hr, the maximum settlement is 30.4 cm near the PVD installation, while the minimum is 27.2 cm near the edge of the cylinder tank.  The results are in agreement with theoretical predictions and previous studies. The maximum settlement is comparable with the settlement calculation using Barron’s method. The settlement variation with distance from the PVD and depth was consistent with stress-distribution theory.