Experimental Study On Effect Of Mixing Sand On Reinforcement Of High Clay Dredger Fill By Vacuum Preloading

With the rapid development of China’s coastal economy and rapid growth of urban population,the shortage of land resources in coastal areas has become increasingly prominent.Sea reclamation with marine sludge has been an important way to solve China’s coastal land resources tensions.As the marine sludge has characteristics of high water content,poor water permeability,high compressibility and low strength,it must be treated after filled by some reinforcement means before it can be used for construction.Vacuum preloading method has been widely used in reinforcement project of high water content soft soil foundation because of its advantages of fast loading speed,short construction time and impossibility of stability losing during reinforcement.However,when reinforcing the high clay dredger fill with vacuum preloading method,because of the pressure difference between the vertical drainage body and the surrounding soil,the fine particles in dredged soil migrate along the hydraulic gradient to the periphery of the vertical drainage body,forming a dense layer with low permeability coefficient.As a result,the soil away from the vertical drainage body can hardly get drainage,causing a undesirable consolidation effect.In order to improve the reinforcement effect of high clay dredger fill with vacuum preloading method,the thesis proposes a method of improving the effect of vacuum preloading by mixing sand into the dredger fill,and conducts a series of related experimental study.In order to study the influence of mixing sand into sludge on the reinforcement effect of high clay dredger fill by vacuum preloading,based on a vacuum preloading soft foundation treatment project,the monitoring and testing indexes of vacuum,surface subsidence,stratified settlement,pore water pressure and vane strength in the test area are analyzed to study the consolidation behavior difference of different stratums.Accordingly,the feasibility of improving the effect of vacuum preloading by sand mixing was discussed.Taking the dredger fill of Dongtou County of Wenzhou,the self-developed small model bucket vacuum preloading model test equipment is adopted to carry a series of contrast tests.Through monitoring,testing,comparing and analyzing the difference of the water displacement,pore water pressure changes during the reinforcement process and the strength and compressibility indexes after reinforcement,the impact of sand mixing rate and sand particle size is studied on the vacuum preloading process and result.The results show that the sand mixing rate has a great impact on the vacuum preloading method.The greater the sand mixing rate ranging from 0 to 15%,the better the drainage effect of soil,the greater the dissipation rate of excess pore water pressure,the lower the moisture content of soil after reinforcement,the greater the vane shear strength,and the lower the compression coefficient.The sand mixing particle size also has certain influence on the effect of vacuum preloading.With the decrease of the mixing particle size from 2.0 mm to 0.075 mm,the displacement of soil samples increased firstly and then decreased,and the strength of the reinforced samples firstly increased and then decreased,reaching the peak at a certain particle size,which means there exists an optimal sand mixing particle size for a specific soil.The result shows that mixing sand into sludge can carry a positive impact on the effect of reinforcement of high clay dredger fill by vacuum preloading,and it has certain reference meaning for the dredger fill soft foundation reinforcement project.