Evaluation of piled-supported structures under extreme scour conditions

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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. **