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

这项快速反应研究(RAPID)奖支持对地震期间钙质砂土液化危险的研究。钙质砂的液化仍然是一项持续的挑战，不仅在夏威夷，2006年的Kiholo湾地震造成Kawahae港疏浚和自然沉积的钙质土壤液化，而且在全球赤道地区也是如此。基础设施的抗震能力，包括港口、海运码头和海军设施，是夏威夷和美国本土经济、应急响应和安全的关键组成部分。钙质砂在几个方面与石英砂不同，包括颗粒内孔隙率、研磨表面、可碎性和可变胶结作用。这些独特的性质意味着，如果不根据基础研究进行修改，已建立的石英砂液化危险性评估关系就不能可靠地用于钙质砂。这项研究将提高夏威夷的防震能力，并有助于更广泛地了解这种当地丰富的材料。本项目的具体目标是：(1)表征夏威夷钙质砂基于应变的液化敏感性关系，并将其与石英砂的已有关系进行比较；(2)考察基于应变的液化敏感性关系对土壤初始状态和有效应力的依赖关系；(3)收集特定场地的锥体贯入尖端阻力和剪切波速度，以与实验室得出的循环强度相关。将使用NHERI@UTexas T-Rex移动振动器进行现场循环测试，以研究循环剪切应变与2m以下超静孔压产生之间的关系。通过将T-Rex应用于螺旋土锚，并将其与特殊阵列的质点速度和孔压传感器一起安装到不同的深度，将获得增强深度振动的方法。现场采样土壤的循环实验室测试将用于表征钙质砂在现场测试的一组扩展条件和初始状态下的循环行为。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.