RAPID: Group Effects on Pile Downdrag Following Liquefaction

1811-1812年新马德里地震序列中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，并在美国历史上最大的国内地震中排名前20位。 这些地震的地震波传播了很长的距离，因为周围基岩的能力，因为地震发生在大陆板块的中间。 在新马德里地震期间，观察到地下水位以下的土壤在震动后暂时变成粘性流体的土壤液化。液化导致作为大多数基础设施的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1811-1812年序列相同规模的地震，这场地震可能会导致美国自然灾害造成的最高经济损失。 由于地震附近地区人口密集（圣路易斯、密苏里州和孟菲斯、田纳西州），因此需要对地震液化引起的土木基础设施的行为有更多的了解，以防止损失。 为了弥补这种缺乏了解的情况，将使用小型炸药在全尺寸条件下产生液化，并测量地基沉降和地基上的向下摩擦力。测试将在阿肯色州的一个场地的两组桩上进行。主要支持将由Nucor Yamata Steel Corperation提供;然而，NSF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）赠款将提供补充资金。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，以产生与测量行为更好的一致性。改进的设计程序将使工程师能够设计出更安全、更具成本效益的基础解决方案，在地震中保持稳定。在Turrell阿肯色州试验场进行的先前研究的局限性将通过以下方式克服：1）测试成组桩而不是单个桩; 2）在爆破前将地基上的静荷载保留较长时间，以允许中性面形成;和3）在爆破后，让地基在较长时间内保持静载，让中立面重新发展。为改善我们的为了了解深层地基上的爆炸引起的下拉/拖曳荷载，将在阿肯色州的一个场地对两个不同的桩组（钢管组、H桩组）进行爆炸引起的液化试验。其目的是测量负表面摩擦力和下拉引起的沉降。通过在桩群顶部施加静荷载，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，以更好地与测量响应相一致。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具有成本效益的基础至关重要，这些基础在未来的地震中是安全的。 从该项目获得的成果将用于减轻具有类似地质剖面的其他地震易发场地的液化引起的破坏。该奖项反映了NSF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。

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.