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 countenneasures such as mattresses of cable tied blocks. None of the flow
altering countenneasures 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 defonnation 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 countenneasure that provides excellent protection is a mattress of cable tied blocks
underlain by a geotextile tied to the pier. Design suggestions are provided for a number of annoring
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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