This report is in fulfillment of NCHRP Project 24-7, Countermeasures to Protect Bridge Piers from Scour. The focus of the report concerns alternatives to standard riprap installations as pier scour countermeasures. Two kinds of countermeasures were examined: flow altering
countermeasures such as sacrificial piles and armoring countermeasures such as mattresses of cable tied blocks. None of the flow altering countermeasures were found to be overly effective. Under flood conditions in sand bed streams, riprap placed in the absence of a geotextile or granular filter
layer was found to gradually settle and lose effectiveness over time even under conditions for which the riprap is never directly mobilized by the flow. This settling is due to deformation and leaching
of sand associated with the passage of bedforms. Riprap performance can be considerably improved with the use of a geotextile, especially if the geotextile is sealed to the pier. Another countermeasure
that provides excellent protection is a mattress of cable tied blocks underlain by a geotextile tied to the pier. Design recommendations are provided for a number of armoring countermeasures.
Includes volumes 1 and 2. Report created in cooperation with Bruce W. Melville, Anna Hadfield, and Christine Lauchlan, University of Auckland, Auckland, New Zealand; Yee-Meng Chiew, Nanyang Technological University, Singapore; Arthur C. Parola and D. Joseph Hagerty, University of Louisville, Kentucky
Prepared for National Cooperative Highway Research Program; Transportation Research Board; National Research Council
Parker, Gary; Toro-Escobar, Carlos; Voigt, Richard L. Jr..
Countermeasures to Protect Bridge Piers from Scour.
St. Anthony Falls Laboratory.
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