Analysis and Evaluation of Single Piles in Laterally Spreading Soil
Liquefaction–induced lateral spreading is an important load case for pile–founded bridges and port facilities located in seismically active regions. This work presents a kinematic analysis of the effects of lateral spreading on a single pile embedded in a layered soil profile and discusses the applicability of conventional analysis methods to the lateral spreading problem. A series of three–dimensional finite element models are created and analyzed using the OpenSees finite element analysis platform developed at the Pacific Earthquake Engineering Research (PEER) Center. The developed FEA considers a single pile (modeled using beam elements) embedded in a soil continuum (modeled using brick elements). Beam–Solid contact elements are utilized to define the interface between the pile and soil elements. Three distinct reinforced concrete pile designs are considered in the models. Elastoplastic behavior is considered in both the pile and the soil through the use of fiber sections and a Drucker–Prager constitutive model, respectively. Each individual component in the model is validated through a series of simple analyses, ensuring that the desired behavior is captured. Force density–displacement (p – y) curves are extracted from the finite element models and compared to several conventional methods for establishing these curves. The characteristic parameters used in this comparison are initial stiffness and ultimate resistance. Additional,
one–dimensional models are created which utilize the same beam elements and consider the soil response through the use of p – y curves generated using both the FEA results and conventional means. The results for the lateral spreading models show that elastoplastic soil behavior must be considered in order to determine appropriate maximum moment demands for piles. Through the extraction of p – y curves from the 3D models, it is determined that the kinematics of the pile greatly influence the extracted curves. A rigid pile undergoing a uniform displacement with depth is the most suitable method for obtaining sensible p – y curves from the models. It is shown that the methods commonly used to establish the characteristic parameters for p – y curves at large overburden pressure (greater depth) estimate values which are in excess of those returned by the finite element models, especially for large pile diameters. In the one– dimensional models, the extracted p – y curves produce moment–curvature demands in piles which are similar to the results of the three–dimensional simulations, while the conventional curves produce demands which do not correlate well with the 3D modeling effort. It is determined that the conventionally–used methods are most applicable for moderately–sized piles subject to loads applied at or above the ground surface, but misrepresent a deeper event such as lateral spreading.