Large Scale Model Tests On Treatment Of High Water Content Dredged Sediment Using The Combined Method Of Flocculation And PHD-facilitated Vacuum Pressure

China produces a large volume of dredged sediment every year,the main treatment methods of dredged sediment are sediment disposal and hydraulic reclamation.However,sediment disposal can cause serious pollution to the marine environment.Compared with sediment disposal,hydraulic reclamation is an ideal way to deal with dredged sediment.Vacuum preloading method with prefabricated vertical drain(PVD)is one of the common methods for treatment of reclaimed soil.However,PVD bending and siltation would happen in the vacuum preloading treatment process.Therefore,based on the traditional vacuum preloading method,the feasibility of using prefabricated horizontal drain(PHD)instead of PVD was studied in this thesis.Through the laboratory model test,the consolidationbehavior of dredged sediment treated by PHD was investigated,and the effect of the flocculant on the method was analyzed.The main contents are as follows:(1)The feasibility of the PHD for dredging sediment with high water content was verified through the laboratory model test,and the control test with PVD was completed.The performance of vacuum preloading using PHD and PVD respectively was analyzed.The results showed that the performance of PHD was better than that of PVD in terms of soil surface settlement,vacuum displacement and final soil moisture content.(2)The laboratory model test of flocculation-horizontal vacuum preloading method with layered-filling was completed and compared with the test without flocculant.The soil settlement,vacuum drainage and pore water pressure were monitored,and it was found thatflocculant polyacrylamide could improve the sediment and consolidation rate of soil.Compared with the test without flocculant,the final soil settlement and the cumulative vacuum drainage were approximately the same.(3)After the end of the vacuum preloading,the vane shear test and final water content of the soil were tested.It was found that the vane-shear strength of the soil with flocculant was higher,and the final water content and grain analysis showed no significant difference from that of the soil without flocculant.