RAPID/Collaborative Research: Investigating the Liquefaction Susceptibility of Calcareous Sand in Hawaii with an Enhanced NHERI@UTexas Large Mobile Shaker

Portland State University, Portland OR

Investigators

Abstract

This Grant for Rapid Response Research (RAPID) award supports investigation of the liquefaction hazard of calcareous sands during earthquake shaking. Liquefaction of calcareous sands remains an ongoing challenge, not only in Hawaii where the 2006 Kiholo Bay earthquake caused liquefaction of both dredged and naturally-deposited calcareous soils at the Kawaihae Harbor, but also globally in equatorial regions. The seismic resiliency of infrastructure, including ports, maritime terminals and naval facilities, is a critical component to the economy, emergency response, and security of Hawaii and the US mainland. Calcareous sands differ from quartz sands in several aspects, including intraparticle porosity, abrasive surfaces, crushability, and variable cementation. These unique properties mean that established relationships for evaluating the liquefaction hazard of quartz sands cannot be reliably used for calcareous sands without modifications based on fundamental studies. This research will improve earthquake preparedness of Hawaii and contribute more broadly to a fundamental understanding of this locally abundant material. The specific objectives of this project are: (1) characterize the strain-based liquefaction susceptibility relationship for Hawaii calcareous sand and compare it to established relationships for quartz sands, (2) examine the dependency of the strain-based liquefaction susceptibility relationship on initial soil state and effective stress, and (3) collect site-specific cone penetration tip resistance and shear wave velocity to relate to laboratory-derived cyclic strength. In situ cyclic testing will be performed with the NHERI@UTexas T-Rex mobile shaker to investigate relationships between cyclic shear strain and excess porewater pressure generation below a depth of 2 m. The enhanced shaking at depth will be obtained by applying T-Rex to a helical soil anchor that is installed along with a special array of particle velocity and pore-water-pressure transducers to various depths of interest. Cyclic laboratory testing on site-sampled soil will be used to characterize cyclic behavior of the calcareous sand under an expanded set of conditions and initial states from the in situ testing. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.