Linear And Non-Linear Analysis Of Single Piles And Pile Groups In Nonhomogeneous Soils

The foundation soil is a sedimentary deposit and a nonhomogeneous medium. In the vertical direction, the foundation soil is layered or the mechanical parameters of the soil vary with the foundation depth. In analyzing the pile-foundation interaction, the nonhomogeneous properties of the foundation should be considered. Thus, the characteristics of the pile-foundation systems in the engineering design can be obtained.In this dissertation, the numerical method for analyzing the pile-foundation interaction is developed for considering the nonhomogeneous properties of the foundation soil. In the proposed numerical method, the generalized Kelvin solutions in a multilayered elastic medium are applied. Thus, the nonhomogeneous properties of the foundation in the vertical direction can easily be analyzed. The interfaces between different soil layers have been considered in the generalized Kelvin solutions, therefore the integral along the interface can be avoided in the proposed numerical method.First, based on the generalized Kelvin solutions, the equations of the shear and displacements at the interface for the foundation soil are established. In establishing the differential equations of the pile under the vertical load, the Bernoulli-Euler theory of the beam is used. Then, the continuous conditions of displacements along the interface of the pile-foundation are utilized for obtaining the overall equations of the pile-foundation interaction. The corresponding programs are written in Fortran 90. The verification of the proposed numerical methods is executed by analyzing the three examples of a single pile and pile groups. It can be found that the results obtained by the proposed method are satisfactory. Using the numerical method, the problems of single piles and pile groups in the layered soil foundation and the Gibson foundation are further analyzed in detail. Some conclusions for elastic conditions and piles loaded by the vertical loads are drawn. These results can be used for pile design and constructions.With the loads on the pile increasing, the lateral shear stresses along the pile increase. The lateral shear stresses are equal to the critical values of the pile-foundation interface, the slipping along the interface of the pile-foundation occur. For considering this phenomenon, the corresponding numerical methods are developed in the proposed numerical method. The verifications by two examples are executed. It can be shown that the proposed method is very effective.The foundation soil in engineering is nonlinear. The mechanical parameters of soil are related to the load magnitudes. This property of the soil should be considered. The Duncan-Chang nonlinear model is selected to further develop the numerical method. The verification by two examples is executed. It can be found that the results obtained by the proposed method can reflect the nonlinear properties of the soils.The optimized design of the pile foundation can be important. It can promote the capability of the loads on the pile, and reduce the numbers, diameters and lengths of the piles. Thus, the best design can be obtained. For this purpose, the proposed numerical method is applied. First, the limit bearing capability of the pile in the nonhomogeneous soil is calculated. Then, the settlement and safety of the pile foundation are checked. Thus, the design of the pile foundation can be optimized. It can be found that the proposed optimized method can obtain the better design.