Laboratory Determination of Efficiency of Prefabricated Vertical Drains Incorporating Vacuum Preloading

This paper is mainly concerned with a laboratory study to investigate the effect of vacuum preloading. Two separate series of tests were conducted in a large-scale consolidation apparatus designed and installed at the University of Wollongong, with axial load increments of 30 and 50 kPa. The first series of tests were performed based on the conventional method (i.e. without vacuum preloading). For the second series, a vacuum pressure of 100 kPa was applied during the process of consolidation. The corresponding settlement behaviour was recorded and plotted. The extent of smear zone was examined by the variation of permeability of small specimens obtained from the large-scale consolidometer. The void ratio-permeability relationship was also determined from the small specimens. The test results based on the large-scale laboratory testing confirm the efficiency of vacuum preloading in comparison with the conventional method of surcharge alone.