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 annoring 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.
University of Auckland; Nanyang Technological University; University of Louisville
Parker, Gary; Toro-Escobar, Carlos; Voigt, Richard L. Jr..
Countermeasures to Protect Bridge Piers from Scour.
St. Anthony Falls Laboratory.
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