Study On Efficiency Factors Of Bearing Capacity And Composite Modulus Of Multi-pile Composite Foundation

The composite foundation method has been widely applied in the engineering practice in the past decades and the experience far precedes the theory of composite foundation. This thesis deals with the efficiency factors of bearing capacity and composite modulus of multi-pile composite foundation.Firstly, the calculation methods of composite foundation and multi-pile composite foundation were summarized. Especially the pile-soil stress ratio,efficiency factors of bearing capacity and composite modulus of multi-pile composite foundation were emphatically introduced.Secondly, analytical formulas for efficiency factors of bearing capacity of multi-pile composite foundation were deduced. Because the design theory and calculation method are immature, the efficiency factors of bearing capacity can not be selected accurately. From the relationship between efficiency factor of soil and pile-soil stress ratio of ordinary composite foundation, and based on the analytical solution of pile-soil stress ratio in multi-pile composite foundation, the general method for calculating efficiency factors of bearing capacity of auxiliary piles and the soil in multi-pile composite foundation was presented in this thesis. By applying the method in practical project, its feasibility was proved.Thirdly, a new calculation method of multi-pile composite foundation was studied. Composite modulus, the basis for calculating the settlement, reflects the ability of composite foundation to resist the deformation; and the composite modulus in the reinforced area is crucial in calculating the settlement of this part. A simple method to calculate composite modulus of multi-pile composite foundation was given at first,but there were considerably errors between calculated and measured results for a practical example. Then the calculation formulas of composite modulus of multi-pile composite foundation, in which the interaction between piles was taken into account, are proposed in this thesis. A case study was carried out with these formulas. And the results were found to be closer to the measured data than those of other methods.Finally, with the help of the nonlinear FEM software package ABAQUS, a numerical simulation of multi-pile composite foundation was made, the pile-soil stress ratios were obtained and they can be the reference for the practical projects.