RAPID: Downdrag Behavior of Piles & Drilled Shafts After Liquefaction

地震震动会导致地下水位以下的松散沙子液化，表现为重液体，导致支撑在浅基础上的建筑物、桥梁和港口下沉、滑动或倾覆。液化造成的直接和间接经济损失是社会的巨大代价。解决这一问题的一种方法是使用深层地基，它可以穿过可液化的沙子，进入不会液化的致密层。然而，液化砂土的沉降仍会对基础墙产生下摩阻力，增加荷载，导致过大的沉降。在没有现场测量的情况下，工程师们不确定会产生多少向下摩擦，以及会发生多少沉降量。由于这种不确定性，使用了相互矛盾的设计程序。为了解决这一问题，将使用小型炸药在全尺寸条件下产生液化，并将测量向下摩擦和地基沉降。测试将在阿肯色州的一个地点的六个不同的基础上进行。主要资金将由阿肯色州公路和运输部提供；然而，来自NSF的补充资金将显著扩大该项目的范围。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，并开发修改以产生与测量的行为更好的一致性。改进的设计程序将使工程师能够设计出安全、但具有成本效益的基础解决方案，这些解决方案在地震期间将保持稳定。为了加深我们对深基础液化下压的理解，将在阿肯色州的一个场地进行三个全尺寸钻孔竖井和三个打入桩(钢管、H型和预应力混凝土)的爆炸液化试验。NSF资金将用于提供静载，该静载将应用于每个测试基础以模拟静载，同时将在液化后测量土壤沉降和桩的沉降。目的是测量负摩阻力和下行阻力引起的沉降。考虑到静载荷，这些试验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，以产生与测量响应更一致的结果。由于深基础是在可液化砂土中支撑结构的常见方法，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。

Earthquake shaking can cause loose sands below the water table to liquefy and behave like heavy liquid, causing buildings, bridges and ports supported on shallow foundations to settle, slide or tip over. Direct and indirect economic losses resulting from liquefaction are substantial costs to society. One solution to this problem is to use deep foundations which penetrate through the liquefiable sand into a dense layer that doesn't liquefy. However, settlement of the liquefied sand can still cause downward friction on the foundation wall, increasing the load and leading to excessive settlement. In the absence of field measurements, engineers are uncertain about the amount of downward friction that will develop and how much settlement will occur. Because of this uncertainty contradictory design procedures are used. To remedy this problem, small explosive charges will be used to produce liquefaction under full-scale conditions and measurements will be made of the downward friction and foundation settlement. Tests will be performed on six different foundations at a site in Arkansas. Primary funding will be provided by the Arkansas State Highway and Transportation Department; however, supplemental funding from NSF will significantly expand the scope of the project. 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 safe, yet cost effective foundation solutions which will remain stable during earthquakes. To improve our understanding of liquefaction-induced downdrag on deep foundations, blast induced liquefaction tests will be performed on three full-scale drilled shafts and three driven piles (steel pipe, H sections, and pre-stressed concrete) at a site in Arkansas. NSF funding will be used to provide the static load that will be applied to each test foundation to simulate dead load while soil settlement and pile settlement will be measured after liquefaction. The objective is to measure negative skin friction and downdrag induced settlement. With the inclusion of a static load, 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.