Evaluation of Lateral Behavior of Pile-Supported Bridges under Scour Conditions

Abstract

Scour is the removal of soils in the vicinity of bridge foundations, resulting in a reduced capacity of the foundations, which may lead to a bridge failure. Scour causes 60% of bridge failures in the United States. To minimize bridge failures, the Federal Highway Administration (FHWA) has established a requirement that all state highway agencies should evaluate whether bridges in their inventory are scour susceptible. Therefore, it is critical that state Departments of Transportation (DOTs) are able to determine quickly and effectively which bridges in their inventories are scour-critical, enabling responsible management of those bridges during and after scour events. It is of importance to identify and explore analytical methods for determining bridge system susceptibility to scour events. However, most research so far has mainly focused on the prediction of scour depth, and limited knowledge is available for the evaluation of bridge performance under scour conditions. In addition, scour by removing soils around bridge foundations changes the stress history of the remaining soils. The change of the stress history however is often ignored in the analysis or design. The objective of this study was to understand potential scour effects on the behavior of laterally loaded piles by considering the stress history of the remaining soils and the scour-hole dimensions. Furthermore, a comprehensive study was conducted to evaluate the lateral behavior of an entire bridge under a scour condition by considering soil, pile foundation, and superstructure interactions. To consider the effects of the stress history change by scour on the behavior of laterally loaded piles, the conventional p-y curves for clays and sands were modified. To examine the effects of the scour-hole dimensions on the behavior of laterally loaded piles, 3D finite difference analysis run in FLAC3D was performed to evaluate the responses of laterally loaded piles under different scour-hole dimensions including scour depth, scour width, and scour-hole slope angle. And one-dimensional simplified methods were developed to address the effects of scour-hole dimensions of the behavior of laterally loaded piles in clays and sands by modifying the p-y curve method based on wedge failure. Finally, analysis of the bridge structures as a whole system was conducted using the integrated analysis program that was developed by integrating Soil Spring Module (SSM) into the structure software, STAAD.Pro. With the integrated analysis program, the analysis of soil-pile foundation-structure interactions was accomplished and the lateral behavior of the bridge was evaluated at different scour depths by considering the change of the stress history of the remaining soils. The analytical results show that scour substantially affected the behavior of laterally loaded piles; however, the scour effects on the lateral behavior of the entire bridge were considerably reduced due to the interactive effects of bridge components within the bridge structure.