| The analysis of deep foundations at the service limit state is important when foundation settlements are critical to the operation of a structure. The "t-z" method is a widely used soil-structure interaction model for the analysis of deep foundation settlement. In current practice, nominal values of soil-structure interface stiffness and strength parameters are used to determine the deep foundation settlement based on the "t-z" method. However, the nominal magnitude and variability of these parameters can vary from one designer or site to another, thus making the settlement results somewhat subjective. By considering reliability-based design principals, probabilistic relationships can be rationally incorporated into the settlement analysis of deep foundations, and thus, design uncertainty can be quantified. Along this approach, Load and Resistance Factor Design (LRFD) procedures may be utilized to develop resistance factors for use in design. Utilizing a "t-z" model and the Monte Carlo simulation process, various types of probabilistic solutions are developed for deep foundation axial capacity at the service limit state. To model the soil-structure interaction, ideal elasto-plastic and hyperbolic load displacement behavior of the soil-structure interface is considered for both total stress (undrained) and effective stress (drained) analyses. Consequently, resistance factors, appropriate for design in AASHTO LRFD applications, are calculated utilizing the developed probabilistic load capacity relationships for deep foundations. A parametric study is completed, in which the geometry of the deep foundation element and the soil-structure interface parameters are varied to understand their effect on the magnitude of the resistance factors. Finally, load displacement data for a series of micropile pullout tests is utilized to demonstrate and validate the developed service limit state probabilistic design approach for standard deep foundation design. |
