Bridge Pier Scour Countermeasures

Local scour at bridge piers is a potential safety hazard to the traveling public and is a major concern for transportation agencies. Bridge pier scour is a dynamic process that varies with water depth, flow angle, pier geometry and other factors. If it is determined that scour at a bridge pier can adversely affect the stability of a bridge, countermeasures to protect the pier should be considered. This paper provides an overview of the results from National Cooperative Highway Research Program (NCHRP) Project 24-07(2). The objectives of the research are to develop and recommend: (a) practical selection criteria for pier scour countermeasures, (b) guidelines and specifications for design and construction, (c) guidelines for inspection, maintenance, and performance evaluation. The countermeasures that were considered included riprap, articulating concrete blocks, gabion mattresses, rigid and flexible grout filled mattresses and partially grouted riprap. Extensive testing was performed for each of the countermeasure types in the 2.4 m flume at the Colorado State University (CSU) — Engineering Research Center hydraulics laboratory to provide guidance on countermeasure thickness, extent, filter requirements, edge treatment, toe down, flexibility, and interconnectivity. A summary of the current state of practice was combined with the results of laboratory testing to provide detailed guidelines on (1) Design and Specification, (2) Construction, and (3) Inspection, Maintenance, and Performance Evaluation for each of the five pier scour countermeasures.