Research On Load Transfer Laws Of Multi-element Composite Foundation With Cushion

Multi-element composite foundation as a new type of composite foundation, its theory is still rather immature. In view of the situation mentioned above, the paper firstly reviews the present studies on the theory of multi-element composite foundation and the effect of cushion in composite foundation, next, based on the result of model tests in door and numerical simulation, the effect on pile load transfer in multi-element composite foundation as to characteristic of cushion is analyzed:1) Laws of stress ratios of pile and soil with different applying loads, load transfer behaviors of the rigid columns and distribution of the rigid pile skin frictions along the pile length are studied in multi-element composite foundation that is made of rigid and flexible columns.2) Numerical simulation of the model tests are presented by FEM software ADINA. Based on the result of numerical simulation, analyzed the bearing capacity and settlement of multi-element foundation with different thickness and modulus of cushion.3) Based on elastic theory, together with the consideration of horizontal interaction between stone columns and soils around the columns, the stress status of the columns in composite foundation with stone column is analyzed with the stress function method and load-settlement relation of the stone column is derived considering soils stress among the columns, self-weights of columns and soils.Compared with the result of model tests and numerical simulation, a series of important conclusions are obtained:1) At the same load level, the settlement of multi-element composite foundation increases with the increases of cushion thickness, however, the settlement of multi-element composite foundation decreases with the increases of cushion modulus.2) Column-soil stress ratio of the both rigid and flexible columns increases with the increases of applying loads.3) Column-soil stress ratio of the both rigid and flexible columns decreases with the increases of the cushion's thickness, however, Column-soil stress ratio of the both rigid and flexible columns increases with the increases of the cushion's modulus. 4) The location of the column's maximum axial force is not at the top of the rigid column, but at some depth under the columns'top. The negative friction stress of rigid column increases with the increasing of applying loads and the point of the maximum axial force moves downwards.5) With the increases of the cushion thickness, stress at the top of rigid column decreases, the negative friction stress of rigid column increases, the section of the negative friction stress increases, and the point of maximum axial force moves downwards. Stress at the top of the flexible column slightly decreases, the point of maximum axial force moves downwards, and the negative friction stress of flexible column appears.6) With the increases of the cushion's modulus, stress at the top of the rigid column increases, the negative friction stress of the rigid column decreases, the section of the negative friction stress decreases, and the point of maximum axial force moves upwards; stress at the top of flexible column slightly increases, the point of maximum axial force moves upwards, and the negative friction stress of the flexible column decreases and then disappears.