Doctor of Philosophy (PhD)
Civil and Environmental Engineering
The design of pile foundations to resist lateral loads is essential in offshore structures and bridge foundations. The lateral behavior of piles has been studied in the past by experimental investigations coupled with analytical and numerical methods. The problem is complex due to the nonlinearities from soil behavior, gap formation, and pile-soil-pile interaction in pile groups (or the group effect). In this work, the finite element (FE) modeling was used to study the lateral behavior of pile groups. The FE method is robust and allows incorporating the necessary aspects for studying the behavior of pile groups. The nonlinear material behavior was incorporated using nonlinear constitutive models. The pile-soil interface was modeled using the zero-thickness surface-surface interaction, which provided the capability for modeling the gap behind the piles, and the transfer of interface normal and frictional stresses. The group interaction was facilitated thru the interaction of stress fields around the piles, and by the continuity of the FE mesh. The lateral behavior of three pile group (PG) configurations (vertical, battered, mixed) with a similar number of piles were evaluated under static and dynamic loading. In the static analysis, the case study of the M19 pier foundation field test was used to verify the FE models. A parametric investigation for the effect of pile spacing and clay soil type was performed. The results showed that the lateral stiffness of the battered and mixed PGs was significantly higher than the vertical PG (+120%, +50%, respectively). The lateral load was found unevenly distributed among the piles in all PGs, and the exterior piles carried 1.5-2% higher load than the interior piles. The influence of the group effect vanished at pile spacings greater than 5D (D is pile width). Also, the influence of pile spacing was more prominent along the load direction. In the dynamic analysis, the PGs behavior was evaluated in barge impact simulations. The results showed that the battered and mixed PGs had similar and large lateral stiffness, which resulted in limited pile cap displacement and large deformation in the barge bow. The weak lateral stiffness of the vertical PG allowed the development of significantly larger impact force and pile cap displacement compared to the battered and mixed PG.
Souri, Ahmad, "Numerical Evaluation of the Lateral Behavior of Vertical and Battered Pile Group Foundations Using 3-D Finite Element Modeling" (2017). LSU Doctoral Dissertations. 4157.