RAPID: Downdrag Behavior of Piles & Drilled Shafts After Liquefaction

地震会导致地下水位以下的松散沙子液化，表现得像重液体，导致浅基础上的建筑物、桥梁和港口沉降、滑动或翻倒。液化造成的直接和间接经济损失是社会的巨大代价。解决这个问题的一个办法是使用深层地基，这种地基可以穿透可液化的沙子，形成不能液化的致密层。但液化砂沉降仍会对基础墙产生向下摩擦，增加荷载，导致过度沉降。在缺乏现场测量的情况下，工程师们无法确定将产生的向下摩擦量以及将发生多少沉降。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，将在全尺寸条件下使用小爆炸药产生液化，并测量向下摩擦和基础沉降。测试将在阿肯色州一个地点的六个不同地基上进行。主要资金将由阿肯色州公路和运输部提供；然而，来自美国国家科学基金会的补充资金将大大扩大项目的范围。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，并进行修改，以使其与测量结果更好地吻合。改进的设计程序将使工程师能够设计出既安全又具有成本效益的基础解决方案，这些解决方案在地震中仍能保持稳定。为了提高我们对深地基上液化引起的下拉的理解，我们将在阿肯色州的一个地点对三个全尺寸钻孔井和三个打入桩（钢管、H型钢和预应力混凝土）进行爆炸引起的液化试验。NSF基金将用于提供静荷载，静荷载将施加于每个测试基础上以模拟恒载，同时将测量液化后的土壤沉降和桩沉降。目的是测量负皮肤摩擦和下阻力引起的沉降。随着静态载荷的加入，这些测试的结果将允许研究人员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好的一致性。由于深层地基是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地基至关重要，这些地基在未来的地震中是安全的。

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.