Risk-based method for selecting bridge scour countermeasures

Bridge engineers are often faced with the task of selecting and designing effective bridge scour countermeasures. The selection of an appropriate countermeasure is dependent on whether the problem is local scour at the pier or abutment, contraction scour across the bed at the bridge opening, reach-wide channel degradation, or lateral channel movement. Confidence in a given countermeasure depends on prior experience in using the measure, cost, maintenance, and the ability to detect failure. The use of countermeasures often introduces uncertainty due to a lack of systematic testing and unknown potential for failure. In this paper, a risk-based method for ranking, comparing, and choosing the most appropriate scour countermeasures is presented using failure modes and effects analysis and risk priority numbers (RPN). Failure modes and effects analysis incorporates uncertainty in the selection process by considering risk in terms of the likelihood of a component failure, the consequence of failure, and the level of difficulty required to detect failure. Risk priority numbers can provide justification for selecting a specific countermeasure and the appropriate compensating actions to be taken to prevent failure of the countermeasure.