As the land reclamation industry develops,the dredged silt will be hydraulically filled thicker and thicker,therefore it is proposed to employ the one-time vacuum preloading method to consolidate the ultra-soft soil ground with medium-thick fill of dredged silt.During the field test,the one-time consolidation improvement of the ultra-soft ground filled with 6～10 m thick of dredged silt is performed by two methods,i.e.vacuum preloading with and without sand cushion.Meanwhile,the vacuum degree,ground settlement,pore water pressure,layered settlement and other regularities are monitored and analyzed.Upon a comparison of shear strength and physical properties of soil mass measured before and after consolidation,it is shown that the ultra-soft ground with medium-thick fill of dredged silt is improved and consolidated remarkably using the one-time vacuum preloading method.In addition,the test results indicate that the two methods of vacuum preloading with and without sand cushion make no significant difference to the consolidation effect.