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膨胀，表现得像重液体一样，导致建筑物、桥梁和港口在浅基础上沉降、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成本。 这个问题的一个解决方案是使用深基础，它穿透可膨胀的沙子进入一个不会膨胀的致密层。 然而，液化砂的沉降仍然会对基础墙造成向下的摩擦，增加荷载并导致过度沉降。 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的摩擦力，以及会发生多少沉降。 由于这种不确定性，使用了相互矛盾的设计程序。 为了解决这个问题，将使用小型炸药在全尺寸条件下产生液化，并测量向下摩擦力和基础沉降。 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的补充资金将大大扩大该项目的范围。 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安全，但具有成本效益的基础解决方案，在地震期间保持稳定。 为了提高我们对深层地基上的爆炸液化引起的下拉阻力的理解，将在阿肯色州的一个现场对三个全尺寸钻孔竖井和三个打入桩（钢管、H型钢和预应力混凝土）进行爆炸液化试验。 NSF的资金将用于提供静荷载，该静荷载将应用于每个测试基础，以模拟恒载，同时将在液化后测量土壤沉降和桩沉降。 其目的是测量负表面摩擦力和下拉引起的沉降。通过包含静态载荷，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。

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.