Bearing capacity and load-deformation characteristics of vibratory driven piles

The objectives of this research were to investigate the driving behavior and load-settlement characteristics of vibratory driven piles. To achieve this goal, a finite difference program, FLAC, was employed to simulate the pile-hammer-soil system. The soil was modeled using a hyperbolic stress-strain relationship with isotropic hardening and Rayleigh damping. Geometric damping in the soil was accounted for through the mesh and the absorbing boundaries. A parametric study was carried out to examine the driving process and post driving load-deformation behavior. The important factors that influence the response of vibratory driven piles, such as initial soil conditions, hammer characteristics, soil model, pile properties, and installation characteristics were investigated. This study focused on vibratory driving in drained sands because vibratory driving of piles is usually more efficient than impact driving in sands. The major factors influencing vibratory driving were found to be the pile/soil interface friction and initial lateral earth pressure for non-displacement piles. For vibratory driving of displacement piles, depth of pile embedment and the soil model used were most important. An initial objective of the study was to use a model based on the concepts of critical state soil mechanics and that could account for the dilative and contractive behavior of soils under vibratory loading conditions. However, this approach was not successful due to the inability to develop a method to dependably sense stress reversal within the inherent noise of the explicit solution scheme. The model was employed successfully to investigate the load/displacement characteristics of piles after installation. Soil arching, and soil modulus were found to have large influence on the bearing capacity of piles. The estimated bearing capacities were compared with values obtained from published empirical formulas for vibratory driven piles