Evaluation of piled-supported structures under extreme scour conditions

冲刷是由水流和海浪引起的土壤侵蚀过程，它影响海滩、堤坝和地基等自然和人为地貌。冲刷不仅会对基础造成土壤支撑的损失，还会导致基础构件的劣化，从而危及结构的完整性和公共安全。冲刷是一个世界性的问题。这已成为桥梁破坏的主要原因。根据Lagagse等人的说法。(2007)，美国60%的桥梁故障是由冲刷造成的。 冲刷条件下的结构行为是一个多学科的课题，需要使用水力学、结构和岩土工程知识。广泛的研究工作集中在冲刷深度的预测、冲刷防护和冲刷监测技术上。也有一些研究侧重于桩基础或桥梁在冲刷条件下的性能。然而，有关冲刷过程中产生的岩土问题的研究报告很少。 从岩土工程的角度来看，冲刷是指在冲刷过程中，当覆盖层被清除时，向未被冲刷的土壤(或剩余土壤)卸载的过程。这一过程导致了土体应力历史和土体性质的变化。在研究桥梁或近海结构物的冲刷敏感性时，通常忽略土体应力历史的变化。此外，另一种简化常常是通过忽略冲坑几何特性的变化来进行的。除了岩土工程问题外，通常从结构工程的角度进行建模还存在过度简化的问题。例如，桥梁性能的评估通常是通过只分析桥梁的一个组件而忽略其他组件来完成的，或者通过使用基础的简化边界条件来分析整个桥梁。 本研究计划的目的是通过理论推导和数值模拟，对上述问题提供全面的理解。具体目标是： 1.考虑冲刷事件中土体应力历史和冲刷坑特性变化的轴向和横向荷载群桩的评估； 2.开发了考虑土体应力历史和冲刷坑特性影响的冲刷条件下桩基分析新程序。 3.开发了考虑土、基础和上部结构相互作用的整体冲刷结构的综合分析过程。 我的研究计划的长期目标是改进桩和桩基结构在极端冲刷下的设计和分析程序，并为面临自然灾害的基础设施的可持续性和弹性做出贡献。

Scour is a process of soil erosion caused by currents and waves, which affects natural and man-made features such as beaches, levees, and foundations. Scour can result in not only the loss of soil supports to foundations, but also the deterioration of the foundation elements, therefore compromising the structural integrity and threatening public safety. Scour is a worldwide problem. It has been the predominant factor responsible for the bridge failures. According to Lagasse et al. (2007), 60% of bridge failures in the United States resulted from scour. Structural behaviors under scour conditions are a multidisciplinary topic requiring the use of hydraulic, structural, and geotechnical knowledge. Extensive research efforts have been focused on the prediction of scour depths, scour protection, and scour monitoring technologies. There are also a number of studies focusing on the performance of pile foundations or bridges under scour conditions. However, very few studies have been reported on the geotechnical problems arising during scouring process. From a geotechnical perspective, scour is a process of unloading to the unscoured soils (or remaining soils) as the overburden is removed over the course of scour. This process results in the change to soil stress history and the soil properties in the remaining soils. When examining the scour susceptibility of bridges or offshore structures, the changes to soil stress history are typically neglected. Moreover, another simplification is often made by ignoring the changes to scour-hole geometric properties. In addition to geotechnical problems, there are over-simplifications in modeling that are often made from a structural engineering perspective. For example, evaluation of bridge behavior is often accomplished either by analyzing only one component of a bridge while ignoring the other components, or by analyzing an entire bridge using simplified boundary conditions for the foundations. The objectives of this research program are to provide a comprehensive understanding of the above-mentioned concerns using theoretical derivation and numerical modeling. The specific targets are: 1. Evaluation of axially and laterally loaded group piles considering changes to soil stress history and scour-hole properties in a scour event; 2. Development of a new program for pile analyses under scour conditions, which allows for considering effects of soil stress history and scour-hole properties. 3. Development of an integrated analysis process for a structure subjected to scour in a holistic manner considering soil, foundation, and superstructure interactions. The long-term goal of my research program is to improve the design and analysis procedures for piles and pile supported structures subjected to extreme scour, and contribute to sustainability and resilience of infrastructures facing the natural hazards.