Lateral Movement Of Soil Between Pvds During Consolidation Of Dredged Silt Under Vacuum Preloading

In recent years,dredged silt is usually used as the basic material source in the eastern coastal areas of China,and prefabricated vertical drains(PVDs)combined with vacuum preloading drainage consolidation is used for foundation treatment.Because of the high water content of dredged silt and the lateral suction produced by drainage plate,uneven settlement between drainage plates occurs,and obvious "soil column" phenomenon is formed around the PVD.Therefore,studying the deformation characteristics of soil between PVDs can not only deepen the understanding of consolidation theory of sand wells,but also have important application value in engineering.Firstly,In order to monitor the movement of soil particles conveniently,an indoor model experiment was designed,in which coarse sand was evenly mixed into the soil as a reference material.Variation of soil particles along the radial distance after the test is presented by the beta kind densitometer.Pore characteristics of soil samples before and after test are compared by scanning electron microscope(SEM)and mercury intrusion porosimetry(MIP).Combined with coarse particles added into the soil as a reference material,migration and aggregation of fine soil particles towards the PVD under the vacuum suction is analyzed.According to the movement of red iron powder bands in the soil,lateral displacement of soil around a single PVD is observed indirectly.Finally,clogging effect considering the migration and lateral displacement of soil on the consolidation characteristics is evaluated through compressibility and permeability of remolded samples taken from the soil after the test.Test results show that the main reason for the pore reduction of the soil near the PVD is the deformation of the soil under the vacuum pressure.And the migration and accumulation of fine soil particles has certain effect on the consolidation of the soil.Secondly,based on particle image velocimetry(PIV),the lateral deformation characteristics of soil between PVDs under lateral suction during vacuum preloading consolidation were studied.The lateral deformation of soil between PVDs was monitored in real time by indoor model experiments.Finally,the deformation characteristics of soil between PVDs subjected to vacuum pressure were investigated and an method was proposed to calculate the lateral displacement.In a model test of dredged slurry,red iron particles were used to indirectly indicate the lateral displacement of soil under vacuum preloading.Test results shown that lateral displacement varied with consolidation time and lateral distance from the PVD.The soil underwent the maximum lateral displacement at a point near the PVD.During vacuum preloading,vacuum suction and earth pressure were introduced to represent the stress state acting on a soil element.Vacuum suction was assumed to decrease with lateral distance from the PVD,while the earth pressure applied by the adjacent soil was considered to rely on the motion of the soil element.Then,the soil between two PVDs was divided into an expansion zone and a compression zone according to the stress state of the soil element.Assuming that the volumetric strain induced by vacuum consolidation is the same as that of one-dimensional consolidation,an approximate method was proposed for calculating induced lateral displacement of soil between two PVDs during vacuum preloading.Through comparison,we found that theoretical calculations were consistent with experimental results.Theoretical calculations showed the location of the maximum lateral displacement of the soil,as well as the influence of initial water content on the lateral displacement.