| Deep foundations such as driven piles and drilled shafts can be subjected to important dynamic loads. Driven piles in particular are loaded dynamically during the installation process. The numerical analysis of such foundations has been traditionally performed using discrete pile and soil models. Although of great usefulness, these models do not detail the motions and stress changes in the soil mass surrounding the pile/shaft. Moreover, if the soil is saturated, they cannot account for the fluid interaction. Problems such as loss of soil strength due to liquefaction cannot be considered.; In the present work, the dynamic analysis of deep foundations installed in saturated soils includes a fully coupled finite element formulation. The saturated soil is modeled, based on the theory of mixtures, as a two phase material. Fluid compressibility is considered. The solid and fluid phases have a coupled behavior and an effective stress analysis is performed to model soil behavior. The nonlinear solution is sought in time domain and kinematic nodal results are obtained for both phases as well as fluid pore pressures. The method was implemented in a multipurpose nonlinear finite element program PlasFEM, being developed in the Geotechnical Engineering Group, Department of Civil Engineering, University of Florida.; Two finite element formulations were analyzed. In the first, solid and fluid kinematic vectors and fluid pore pressure are considered continuous and are evaluated at the nodal points (u-p-U). A reduced formulation with discontinuous pore pressure distribution (u-U) was compared with the prior. Results suggest a smoother pore pressure time history for (u-U) but this formulation presents difficulties near fluid incompressibility, where a penalty formulation is required.; The program was used to analyze one and two dimensional initial value problems, where closed form solutions are known. Wave propagation in saturated porous media, in both 1-D and 2-D domains, was modeled and results capture the presence of two compressive and one rotational wave. Short term transient loading conditions (earthquake, blast, pile driving) can be modeled as well as diffusive phenomena such as consolidation.; Pile driving in saturated soil was modeled to study pile-soil interaction. The effects of energy dissipation, stress change in the soil, generation and dissipation of pore pressures, evaluation of potential "freeze," and wave propagation to adjacent structures were investigated. Results show good agreement with field data from pile driving tests, where measured waves in the piles were accurately predicted. |
