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）拨款支持对地震中钙质砂的液化危险进行调查。钙质砂的液化仍然是一个持续的挑战，不仅在夏威夷（2006年基霍罗湾地震导致卡哇海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。包括港口、海运码头和海军设施在内的基础设施的抗震能力是夏威夷和美国大陆经济、应急响应和安全的关键组成部分。钙质砂与石英砂在几个方面不同，包括颗粒内孔隙度、磨粒表面、可破碎性和可变胶结性。这些独特的性质意味着，如果不根据基础研究进行修改，现有的石英砂液化危险性评价关系就不能可靠地用于钙质砂。这项研究将改善夏威夷的地震准备工作，并为更广泛地了解当地丰富的材料做出贡献。该项目的具体目标是：(1)表征夏威夷钙质砂基于应变的液化敏感性关系，并将其与已建立的石英砂关系进行比较；(2)检验基于应变的液化敏感性关系对初始土壤状态和有效应力的依赖性；(3)收集特定场地的锥形穿透尖端阻力和横波速度，以与实验室推导的循环强度相关联。现场循环试验将使用NHERI@UTexas T-Rex移动式振动筛进行，以研究2米深度以下循环剪切应变与超孔隙水压力之间的关系。通过将T-Rex应用于螺旋土锚，可以获得深度增强的震动，螺旋土锚与一组特殊的粒子速度和孔隙水压力传感器一起安装在不同的感兴趣深度。对现场取样土壤的循环实验室测试将用于表征石灰质砂在扩展条件下的循环行为和原位测试的初始状态。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.