Cushion Techniqe And Interaction Between Reinforcements And Surrounding Soil In Composite Foundation

It is important research content for the action mechanism of the cushion and the interaction between reinforcements and surrounding soil in composite foundations. Understanding fully the action mechanism of the cushion and the interaction relation between reinforcements and surrounding soil in composite foundations, it is help to analysis the bearing capacity and settlement of composite foundations, to create new techniques and method of ground improvement, to adopt effectively the composite foundation types.In this paper, two typical types composite foundations, the ground with granular columns and the ground with compressible piles, the action mechanism of the cushion were systematically studied by means of theoretical analyses and numerical analyses, laboratory tests, in-site tests. It possesses important guidance meaning to determine the cushion thickness and materials, to design of composite foundations.For the action mechanism of the cushion, based on the work characteristic of interaction for pile-soil-cushion, and introduced concept of the equality sinking-surface, the harmony equation of the vertical displacement for interaction between piles and surrounding soil were established. Influence of the cushion thickness and materials on properties of the composite foundations were summarized. Theoretical basis to determine the cushion thickness and materials were offered.For the composite foundation with granular columns, based on elastictheory and Mohr-Coulomb yielding criteria, process of lateral interaction between piles and surrounding soil, restriction of surrounding soil and influence of surrounding soil on piles were studied. Analytical formulae of the pile-soil vertical deformation and stress ratio were obtained. Formula exerting load on pile were derived too at ultimate equilibrium state for surrounding soil.New concept of the composite foundation with granular columns of variable cross section is presented. Comparing granular columns of variable cross section with granular columns of uniform cross section, as both lateral restricted ability and area replacement ratio of granular columns for shallow part are improved, bearing capacity for composite foundation and granular columns can be improved. At the same time, based on influence of shear force on the pile-soil interface, and interaction between granular columns with variable cross section and surrounding soil was treated as space and simplify plane problem, calculation methods of bearing capacity for composite foundation and granular columns with variable cross section are studied, respectively.For composite foundation with compressible piles, based on displacement harmony condition, and combining with load transfer method and approximate solution of differential equation, analysis methods of linear and nonlinear interaction between piles and surrounding soil were suggested. A lot of significative results, for example availability pile length, load distribution between piles and surrounding soil, load distribution among all piles under rigidity pile-cap, load-settlement relation etc, were obtained.For composite foundation with compressible piles group, based on displacement harmony condition, mechanics theory and appropriate displacement model, analytical method of interaction between piles group and surrounding soil were put forward under flexible foundation, analytical formula which calculates deformation reinforced area were obtained, Theoretical basis to calculating settlement for composite foundation with compressible piles were offered.No displacement at the infinite location is the true boundary condition for the composite foundation with compressible piles under loads, but it is difficult for the conventional finite element to satisfy exactly this boundary condition. On the contrary, the infinite element is very convenient and effective to reflect the far field effect of the soil in an infinite domain. The key to the infinite element is to determine the nodal shape functions and the assumed elemental displacements. So...