RAPID: Group Effects on Pile Downdrag Following Liquefaction

RAPID：液化后桩下拖力的群效应

• 批准号: 2006323
• 负责人: Richard Coffman
• 金额: $ 7.5万
• 依托单位: University of Arkansas
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-12-01 至 2021-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2006323&HistoricalAwards=false
• 关键词: RAPID; Group; Effects; Pile; Downdrag

Several of the earthquakes that occurred during the 1811-1812 New Madrid earthquake sequence were identified by the United States Geological Survey as being the largest earthquakes East of the Rocky Mountains and within the top 20 of the largest domestic earthquakes United States history. The seismic waves from these earthquakes propagated for a great distance because of the competency of the surrounding bedrock, and because the earthquakes occurred in the middle of the continental plate. Soil liquefaction, where soil below the water table temporarily becomes a viscous fluid following shaking, was observed to occur during the New Madrid earthquakes. Liquefaction results in a loss of strength in the soil that serves as the bearing material for most infrastructure. If the same size earthquake as the 1811-1812 sequence were to occur today, the United States Federal Emergency Management Agency warns that the earthquake could result in the highest economic losses due to a natural disaster in the United States. Because the areas near the earthquake are now densely populated (St. Louis, Missouri, and Memphis, Tennessee) additional understanding of behavior of civil infrastructure when exposed earthquake induced liquefaction is needed to prevent loses. To remedy this lack of understanding, small explosive charges will be used to produce liquefaction under full-scale conditions and measurements will be made of the foundation settlement and the downward friction force on the foundations. Tests will be performed on two pile groups a site in Arkansas. Primary support will be provided by Nucor Yamata Steel Corperation; however, supplemental funding from NSF will significantly expand the scope of the project. This Rapid Response Research (RAPID) grant will provide that supplemental funding. The results from these tests will allow engineers to evaluate the accuracy of existing design procedures and develop modifications to produce better agreement with measured behavior. Improved design procedures will allow engineers to design safer yet cost-effective foundation solutions that will remain stable during earthquakes. Limitations of the previous study at the Turrell Arkansas Test Site will be overcome by 1) testing groups of piles instead of individual piles, 2) leaving the deadload on the foundations for a longer period of time prior to blasting to allow the neutral plane to develop, and 3) leaving the deadload on the foundations for a longer period of time after blasting to allow the neutral plane to redevelop.To improve our understanding of liquefaction-induced downdrag/dragload on deep foundations, blast induced liquefaction tests will be performed on two different pile groups (steel pipe group, H-pile group) at a site in Arkansas. The objective is to measure negative skin friction and downdrag induced settlement. With the inclusion of a static load placed on top of the pile groups, the results from these tests will allow researchers to evaluate the accuracy of existing design recommendations and develop modifications to produce better agreement with measured response. Because deep foundations are a common approach for supporting structures in liquefiable sands, reliable design approaches are critical to provide cost-effective foundations that are safe in future earthquakes. The results obtained from this project will be used to mitigate liquefaction induced damage at other earthquake prone sites with a similar geologic profile.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.

1811-1812 年新马德里地震序列期间发生的几次地震被美国地质调查局确定为落基山脉以东最大的地震，并且位列美国历史上最大的国内地震前 20 名。 由于周围基岩的能力，并且地震发生在大陆板块中部，这些地震产生的地震波传播了很长的距离。 新马德里地震期间观察到发生了土壤液化现象，即地下水位以下的土壤在震动后暂时变成粘性液体。液化会导致作为大多数基础设施承载材料的土壤强度损失。美国联邦紧急事务管理局警告说，如果今天发生与 1811 年至 1812 年序列相同规模的地震，此次地震可能会导致美国自然灾害造成的最高经济损失。 由于地震附近的地区现在人口稠密（密苏里州圣路易斯和田纳西州孟菲斯），需要进一步了解暴露的地震引起的液化时民用基础设施的行为，以防止损失。 为了弥补这种认识上的不足，将使用小型炸药在全尺寸条件下产生液化，并对地基沉降和地基上的向下摩擦力进行测量。测试将在阿肯色州一个地点的两个桩群上进行。主要支持将由纽柯山田钢铁公司提供；然而，国家科学基金会的补充资金将显着扩大该项目的范围。这项快速反应研究 (RAPID) 拨款将提供补充资金。这些测试的结果将使工程师能够评估现有设计程序的准确性并进行修改，以与测量的行为产生更好的一致性。改进的设计程序将使工程师能够设计出更安全且具有成本效益的基础解决方案，并在地震期间保持稳定。先前在阿肯色州特雷尔试验场进行的研究的局限性将通过以下方式克服：1）测试桩组而不是单个桩，2）在爆破前将静载留在地基上较长时间，以使中性面形成，以及 3）在爆破后将静载留在基础上较长时间，以使中性面重新发展。为了提高我们对深基础上液化引起的下阻力/阻力载荷的理解，爆炸诱导液化试验将在阿肯色州的一个地点对两个不同的桩组（钢管桩组、H 型桩组）进行。目的是测量负表面摩擦力和向下阻力引起的沉降。通过在桩群顶部施加静载荷，这些测试的结果将使研究人员能够评估现有设计建议的准确性，并进行修改以与测量的响应产生更好的一致性。由于深基础是在可液化砂中支撑结构的常用方法，因此可靠的设计方法对于提供在未来地震中安全的、具有成本效益的基础至关重要。 该项目获得的结果将用于减轻具有类似地质概况的其他地震易发地点的液化引起的损害。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。