RAPID: Large-Scale Shake Table Test to Quantify Seismic Response of Helical Piles in Dry Sand

This Rapid Response Research (RAPID) project investigated the seismic behavior of helical piles by means of shake table tests on full-scale piles in the UC San Diego laminar soil box. Helical piles are deep foundation elements that look like, and are installed like, a large steel soil screw - they have a slender steel shaft with any number of round plates welded to the central shaft at the tip to provide support to the structure they hold. Helical piles are spun into the ground with a large torque motor and provide support through soil bearing on the plates and along the shaft. They come in many lengths and are often the foundation of choice for retrofitting existing buildings or new, urban construction, due to their small footprint and ability to create minimal disturbance to surrounding structures. Even though it is known from anecdotal studies (e.g., New Zealand and Japan) that piles with comparatively small cross-section and high anchoring capacity, such as helical piles, are beneficial for seismic resistance seemingly due to their slenderness, higher damping ratios, ductility, and resistance to tip uplift, building codes and current state of practice have not been adequately developed for this pile type because no quantitative data exist. Research of seismic behavior of helical pile supported structures is therefore imperative to generate necessary data that will help ensure that helical piles are being correctly applied in seismic areas and establish quantifiable benefits and/or limitations of helical pile use in seismic areas. This project will benefit people living in seismic zones by educating engineers with full-scale helical pile experimental data so that they better understand how to design a building system that is safer, more resilient and sustainable for individuals and the community.