Evaluation of Field-Based Liquefaction Approaches for Calcareous Sands Using Shear Wave Velocity

该项目的目标是评估目前基于现场的液化方法对钙质砂的适用性。这一点很重要，因为在以钙质砂岩为基础的高地震地区(例如海地、波多黎各、夏威夷等)有许多沿海社区，而现有的实地方法几乎完全是为硅质砂的个案研究而开发的。我们将在波多黎各西部的两个地点进行现场和实验室联合测试计划，这是一个理想的地点，因为整个岛屿都有钙质沉积物，该地区的地震活动相对较高，人口密度较高，以及研究团队对这些特殊土壤的专业知识。现场测试计划将包括常规钻井和取样技术、标准贯入测试与锤击能量测量，以及圆锥贯入测试与剪切波速测量。实验室测试计划将包括带有剪切波速测量的循环三轴和循环单剪试验。PIS的研究表明，循环阻力与剪切波速(CRR-vs)之间的关系是土性的，可以用来将现场试验结果与实验室确定的CRR值联系起来。剪切波速(Vs)已被证明是应力和组构的综合效应的一个很好的量度，并假设将样品固化或制备到Vs值原位产生原位CRR。这种方法将通过将实验室和现场的横波速度联系起来，然后将其与现有的基于现场的方法(SPT，CPT)预测的CRR值进行比较，来估计每个地点的现场CRR值。这项研究将有助于更好地理解现有的基于现场的液化势评估相关性如何适用于在许多热带和亚热带沿海地区可以发现的钙质砂岩。此外，该项目将建立在现有研究的基础上，这些研究表明，在实验室和现场适当测量的横波速度可以在实验室测试和现场测量之间提供联系，以表征难以取样的土壤的现场行为。这项研究的主要社会影响将是通过改进目前钙质砂岩液化潜力评估的方法，帮助将地震造成的损失降至最低。该项目的另一个重要组成部分是将代表人数不足的群体的学生纳入STEM研究领域。三名来自波多黎各的拉美裔美国学生将参与这一研究项目。一位来自波多黎各的拉美裔美国人目前是罗德岛大学的博士生，将完成她关于这项拟议研究的论文。作为联邦公路管理局Dwight D.Eisenhower奖学金计划的一部分，两名本科生将作为暑期研究助理参与这个项目，这是国际公路协会、波多黎各大学马亚圭兹大学和罗德岛大学运输中心之间的现有合作。

The objective of this project is to assess the applicability of current field-based liquefaction approaches for calcareous sands. This is of importance because there are many coastal communities in areas of high seismicity founded on calcareous sands (e.g. Haiti, Puerto Rico, Hawaii, etc.), and existing field-based approaches were developed almost entirely for case studies in silica sands. We will perform a combined in situ and laboratory-testing program at two sites in western Puerto Rico, which is an ideal site because of the extent of calcareous deposits throughout the island, the relatively high seismicity of the region, the high population density, and the expertise of the research team with these particular soils. The in situ testing program will consist of conventional drilling and sampling techniques, Standard Penetration Tests with hammer energy measurements, and Cone Penetration Testing with shear wave velocity measurements. The laboratory-testing program will consist of cyclic triaxial and cyclic simple shear tests with shear wave velocity measurements. Research by the PIs has shown that the relationship between cyclic resistance and shear wave velocity (CRR-Vs) is soil specific and can be used to link in situ test results with laboratory determined values of CRR. Shear wave velocity (Vs) has been shown to be a good measure of the combined effects of stress and fabric, and it is hypothesized that samples consolidated or prepared to in situ values of Vs yield the in situ CRR. This approach will be used to estimate the in situ CRR at each site by linking the shear wave velocity in the laboratory and the field, and then comparing this with values of CRR predicted from existing field based approaches (SPT, CPT). This research will lead to a better understanding of how existing field based correlations for the assessment of liquefaction potential, which is the state-of-the-practice in geotechnical earthquake engineering, applies to calcareous sands that can be found in many tropic and subtropical coastal regions. In addition, this project will build upon existing research that shows that shear wave velocity measured appropriately in the laboratory and in situ can provide a link between laboratory testing and field measurements for characterizing the in situ behavior of soils that are difficult to sample. The primary societal impact of this research will be to help minimize losses from earthquakes by improving the current methods for liquefaction potential assessment in calcareous sands. Another important component of this project is the inclusion of students from underrepresented groups in the STEM fields of research. Three Hispanic American students from Puerto Rico will be working on this research project. One Hispanic American from Puerto Rico is currently a Ph.D. student at the University of Rhode Island and will complete her dissertation on the proposed research. Two undergraduates will work on this project as summer research assistants through an existing collaboration between the PI, University of Puerto Rico Mayaguez, and the University of Rhode Island Transportation Center as part of the Federal Highway Administration Dwight D. Eisenhower Fellowship Program.