The Study Of Deformation Characteristics On Reclaimed Soil Foundation Under Vacuum Preloading

With the development of economy, the land resource is increasingly scarce.Reclamation project has been an important way to obtain land resources in manycountries and regions. Reclamation engineering not only enables obtain valuable landresources in the coastal city, but also can solves the dredging problem of sea channel.And it has become the important way to promote the port construction of coastal cityand the development of economic. Reclaimed soil foundation has a engineeringcharacteristic of low strength, high sensitivity, large settlement, long consolidationtime and bad soil structure. Vacuum preloading method has great advantages in theimprovement of reclaimed soil foundation and has been applied widely. In order tofurther promote the vacuum preloading technique in soft soil foundation treatment,this paper combines the indoor model test with the finite element method to analyzedetailedly the consolidation of reclaimed soil foundation under vacuum preloading.The main conclusions are as follows:(1) Using modified triaxial apparatus to carry on vacuum model test, the paperinvestigate the deformation of dredger fill with vacuum preloading. The test apparatuscan stage loading to soil samples and can measure the test sample’s volume change.From the test it can be concluded that the higher the water content of soil sample invacuum loading, the more obvious reinforcement effect is. The change of void ratio isconsiderable. The compression curve under negative pressure has the same rule as ifpositive pressure in which e decreases linearly with the ln p.(2) According to the Biot consolidation theory, established3D axial symmetricmodel which is used to calculate the consolidation of reclaimed land under vacuumpreloading. The FE model takes the modified Cambridge model which takes thepermeability coefficient nonlinear with void ratio of soil into account. The FEAresults are consistent with the indoor test of pore pressure. The results indicate thatthis calculation model can be better analytical in soft soil foundation consolidationdeformation under vacuum preloading.(3) During the vacuum loading, the soils which is close to the plastic drainageboard and the sand cushion is compacted firstly. The soils that parallel to the direction of plastic drainage board almost have the same void ratio. The void ratio of the soil isincreased in a direction perpendicular to the direction of plastic drainage board.Permeability coefficient of the soils which is close to the drainage plate palys a keyrole in the reclaimed soil foundation’s average coefficient of permeability, which willleading to slow the consolidation of reclaimed land.(4) FEM with the constant permeability is used to analysis reclaimed soilfoundation consolidation under vacuum preloading. The results and the test resultshave a great deviation. Therefore when investigated the reclaimed soil foundationconsolidation deformation, consider that the change of permeability coefficient in theconsolidation process is necessary.