Abstract:
Helical piles are one of the pre-manufactured deep foundation types that are commonly used to underpin foundations suffering from excessive settlements. The application of helical piles is growing in urban areas given the fact that the installation process does not generate any vibration, causes minimum site disturbances, imposes low mobilization costs, can be installed in low-headroom areas with portable equipment, and no soil spoils is produced. Although some recent studies have demonstrated the satisfactory behavior of helical piles under seismic loading in dry soils and their dampening nature, the response of helical piles in liquefiable grounds is not yet well understood. The objective of this research was to evaluate the efficacy of helical piles in mitigating liquefaction-induced settlement of shallow rigid foundations and investigate their seismic performance in liquefiable grounds. Two large-scale shake table test series, one without any mitigation measure and one using helical piles, were conducted using the shake table facility at the University of California, San Diego. Each model comprised three soil layers measuring about 10 ft in height and included a shallow rigid foundation seated over an unsaturated crust layer underlain by saturated loose and dense layers. The model ground was based on similar subsurface ground conditions observed in recent earthquakes in New Zealand, Japan, and Turkey where shallow liquefiable soil layers imposed significant damage to the building foundations. The models were extensively instrumented using a wide range of sensors to capture the dynamic response of the soil-foundation-pile system. The experimental results overall illustrated the enhanced seismic behavior of the soil-foundation-pile system response such as reduced excess pore-water pressure generation around the helical piles which was attributed mainly to the densification around the piles during installation. In addition, the foundation supported on helical piles underwent almost no foundation differential settlement and tilt. This study illustrates that helical piles are a reliable and highly efficient measure to mitigate liquefaction-induced foundation tilt and settlement. For future studies, it is recommended the seismic design methods for helical piles be developed for incorporation in design guidelines.