Improvement of dredger fill by stepped vacuum preloading combined with stepped voltage electro-osmosis

The use of vacuum preloading combined with electro-osmosis (VP-EO) to treat dredger fill from seabed has been studied extensively. However, there remain some drawbacks to this method, such as clogging outside of the prefabricated vertical drains (PVDs) and the inhomogeneous consolidation of soil. A novel method for stepped vacuum preloading combined with stepped voltage electro-osmosis (SVP-SVEO) was proposed in this study to overcome these drawbacks, and the influence of the steps of stepped vacuum preloading (SVP) on soil treatment was examined. Five laboratory tests were performed on a dredger fill to evaluate the effectiveness of SVP-SVEO. The vacuum pressure, electric current, volume of extracted water, and average surface settlement were monitored during the tests. After the tests, the water content, shear strength, and electrode corrosion were measured; in addition, scanning electron microscopy (SEM) test of the filter membranes of the PVDs was conducted. The results indicated that SVP-SVEO effectively alleviated the clogging of PVDs and improved the uniformity of soil consolidation. Our results also revealed that SVP-SVEO with three SVP steps yielded better soil reinforcement effects than other methods.