Abstract: vacuum loading mode are generally not considered in Traditional vacuum preloading method in the reinforcement of soft soil. This paper carried out indoor model test, it tested four groups of the flow mud soil samples the water content of which is 100%, the vacuum loading mode are -80 kPa, -60 kPa→80 kPa, -40 kPa→-80 kPa, -20 kPa→-80 kPa, Water, settlement and lateral deformation was monitored during the loading of the sample in the course of the test, and changes of the water content, plasticity index and vane strength was studied after the test. The test results showed that: (1) Vacuum loading mode significantly effects on consolidation of dredger fill flow mud. (2) Soil settlement is largest and strength is highest when the initial vacuum value of -20 kPa better than the others; soil settlement is smallest, and strength is lowest when the initial vacuum value of -80 kPa better than the others. (3) From the distribution characteristics of the plasticity index, soil particles move with water in the soil discharge, initial vacuum load value larger this trend is more obvious; the part of the soil particles will accumulate around of plastic vertical drain and so as to reduce soil permeability; severe cases will affect soil consolidation of follow-up. Finally, it is recommended that a lower initial load mode to loading in the flow mud vacuum consolidation process.

Key words: vacuum preloading, model test, flow mud, initial vacuum load, loading mode, soil particle moving, soil consolidation effect