Field Test And Numerical Analysis Of Vacuum Combined Surcharge Preloading

Vacuum combined Surcharge Preloading is effective way to improve soft ground, this method has many advantages so that it has been widely used in ground improvement project such as irrigation projects, traffic projects, civil projects. The research on design theory and construction technology of vacuum combined surcharge preloading has got great development, but comparing with engineering practice, many theoretical problems need to be solved in the future.This paper was based on Vacuum combined Surcharge Preloading of soft ground in Kang Bo village in Chang Shu. Through in-site monitoring and data analyzing, the change regularity of ground settlement and pore pressure was analyzed. In additional to that, the parameters of soil used in simulation was got in laboratory, two dimension numerical analysis for vacuum combined surcharge preloading was made, and the factors relating to degree of treatment were analyzed. The main work and results were as follows:(1) The change regularity of ground settlement, horizontal displacement and pore pressure was analyzed, the theory of this method for soft-ground treatment was researched. Through in-site test and theoretical calculation, specific penetration resistance (Ps) of silt was increased at65.9%, soil bearing capacity was increased by more than50%, average degree of consolidation reached88.2%, the result met design standard. According Au/Ap curve, the max of Au/Ap reached0.9meanwhile ground is safety, so the result can be considered by similar project to control the preloading speed.(2) The strengthening principles of vacuum preloading, surcharge preloading, vacuum-surcharge preloading are analyzed relatively from stress, deformation, stress path. The results showed that vacuum-surcharge preloading has the greatest effect on soft ground treatment.(3) Comparing Mohr-Coulomb model with Cambridge model, the Cambridge model has more advantages than Mohr-Coulomb in finite element calculation for vacuum combined surcharge preloading. Summarizing calculation method of sand drain ground in two dimensions, which showed that sand wall ground can reflect the pore pressure of ground well, so the two dimensions FEM method is feasible.(4) The vacuum combined surcharge preloading project was studied by ABAQUS FEM program, and the factors relating to degree of treatment were analyzed, the results showed that the higher degree of vacuum can improve treatment effect of soft ground, in the depth of drain board, the well drain board’s drainage ability is, the quicker the speed of ground settlement is. and the more quickly vacuum was transferred. The surface settlement of ground was increased with distance of drain board reduced, reducing distance of drain boards can improve the speed of drainage and low excess pore water pressure quickly, the drain boards should go through soft soil layer, but only increasing the depth of drain board could not get expectant effect of treatment.