Seismic Performance of Steel Helical Piles

Recent earthquakes have highlighted the need for safe and efficient construction of earthquake resilient structures. Meanwhile, helical piles are gaining popularity as a foundation for new structures and retrofitting solution for existing deficient foundations due to their immense advantages over conventional driven pile alternatives. In addition, helical pile foundations performed well in recent earthquakes, proving they can be a suitable foundation option in seismic regions. The objective of this thesis is to evaluate the seismic performance of helical piles by conducting full-scale shaking table tests and nonlinear three-dimensional numerical modeling using the computer program ABAQUS/Standard. The experimental setup involved installing ten steel piles with different configurations and pile head masses in dry sand enclosed in a laminar shear box mounted on the NEES/UCSD Large High Performance Outdoor Shake Table. The loading scheme consisted of white noise and two earthquake time histories with varying intensity and frequency content. The performance of different moment curve fitting techniques used for reduction of shake table experimental data are compared. The experimental results are presented in terms of natural frequency and response of the test piles. The effects of the loading intensity and frequency and the pile’s geometrical configuration and installation method were evaluated. The dynamic numerical model constructed accounted properly for the test boundary conditions, employing tied vertical boundaries. In addition, the nonlinear behavior of the soil during the strong ground motion was simulated by considering a strain-dependent shear modulus and applying Masing’s loading-unloading rules by the overlay method to account for the soil non linearity more realistically. The numerical model was verified employing the full-scale experimental results, then was used to conduct a limited parametric study that investigated the effect of pile stiffness and the location of helix on its lateral response. The experimental results show that the natural frequency of the driven pile was slightly higher than that of the helical piles. However, the response of the helical pile was close to that of the driven pile, which illustrates the ability of helical piles to perform as good as conventional piles under seismic loading