Local scour at bridge piers is a potential safety hazard to the traveling public and is a major concern to transportation agencies. Bridge-pier scour is a dynamic phenomenon that varies with water depth, flow angle, pier shape and width, and other factors. If it is determined that scour at a bridge pier can adversely affect the stability of a bridge, scour countermeasures to protect the pier should be considered. Because of their critical role in ensuring bridge integrity, and their potentially high cost, it is important that the most appropriate countermeasures be selected, designed, and constructed.
NCHRP Project 24-07, "Countermeasures to Protect Bridge Piers from Scour," was completed in July 1999. Project 24-07 involved extensive laboratory testing of riprap, cable-tied blocks, grout-filled bags, permeable sheet piles, pier-attached vanes, and submerged vanes. The laboratory testing demonstrated an enhancement in the performance of riprap and cable-tied blocks when used in conjunction with a geotextile filter. Other countermeasures investigated were shown to be less effective in resisting scour. Several countermeasures such as grout-filled mats, gabions, partially grouted riprap, and geotextile sand containers were not investigated. The results of Project 24-07 provided significant insight into the behavior of the tested countermeasures; however, additional research and field validation of countermeasure performance is needed to develop specific countermeasure selection criteria, guidelines, and specifications.
The objective of this research is to develop and recommend practical selection criteria for bridge-pier scour countermeasures, guidelines and specifications for design and construction, and guidelines for inspection, maintenance, and performance evaluation.
The countermeasures to be considered include riprap, partially grouted riprap, cable-tied blocks, gabions, grout-filled bags and mats, and geotextile sand containers (used as a stand-alone countermeasure or as a filter).
Product Availability: NCHRP Report 593
, a spreadsheet containing an interactive version of the countermeasure selection methodology
, and the Reference Document containing detailed laboratory testing results and translations of three German "Code of Practice" documents