Experimental Study On Dewatering Of High-water-content Dredged Slurry By Flocculation-horizontal Vacuum Twostaged Method

With the strengthening of China’s environmental management efforts in recent years,the dredging projects of ports,waterways,inland rivers and other water areas have produced a large amount of high-water-content dredged slurry.As a efficient slurry dewatering method,the vacuum preloading with prefabricated drains has been widely used in engineering practice in recent years.However,the traditional vacuum preloading with prefabricated vertical drains method still has some shortcomings such as bending of the prefabricated drains,difficulty in construction when dealing with high water content slurry and clogging of the prefabricated drains.In view of the above problems,the feasibility of vacuum preloading method by prefabricated horizontal drains(PHD)which was improved from the vacuum preloading method by prefabricated vertical drains(PVD)was studied in this thesis,and a two-stage method of flocculation and horizontal vacuum for the high water content dredged slurry was proposed.And the best construction conditions of the method was explored through indoor model test.The main research work of this article is as follows:(1)The difference of sediment dewatering between the PVD and PHD under the conditioning of flocculant was studied.the dewatering characteristics of sediment by PVD and PHD,the settlement of soil and deformation of drains were analyzed.The test results show that PVD has a faster dewatering rate in the early stage of vacuum preloading,but decreases faster,whereas the PHD can maintain stable and efficient dewatering for a long time,and the final drainage volume is about 30% higher than that of PVD test.The PVD is severely deformed at the end of the test,and the soil settlement is severely uneven.On the contrary,PHD has almost no deformation and the soil settlement is more uniform.(2)The influence of different amount of flocculant on the dewatering was explored by model test.The characteristics of soil deformation under various test conditions,the change of soil strength after consolidation and the change of particle size distribution were analyzed.The study found that the addition of flocculant improves the composition of soil particles,improves the proportion of coarser grains and the strength of the soil,improves the consolidation and dewatering efficiency of the soil,and there is an optimal dosage of flocculant.The optimal dosage of APAM is 0.45% of dry soil weight in this study.(3)The effect of static deposition time and vacuum loading mode on soil consolidation and soil strength was explored through model tests.The test results show that optimal static deposition time is 24 hours.When different levels of vacuum loading methods are used,the final drainage effect is best in the case of two-stage loading.When using two-stage vacuum loading,increasing the first-stage loading pressure can significantly improve the drainage effect during the first-stage loading,and can improve the soil strength within a certain range.