Placing coarse riprap stones around bridge piers is one method of dealing with pier-scour problems. This study investigates the stability of a riprap layer around a cylindrical bridge pier. Experiments performed in a laboratory flume generated three different modes of riprap failure. These failure modes act singly or combine to cause complete failure of the riprap layer. The failure modes are riprap shear failure, winnowing failure, and edge failure. A semiempirical method to size stones for riprap protection is proposed. The procedure for this method is demonstrated with field data from three separate bridge sites. The experimental data reveal that a thick riprap layer can prevent winnowing in the absence of a filter layer. In addition, a thick riprap layer can sustain a partial breakup with the capability of rearmoring the scour hole, preventing total disintegration of the riprap layer. The author concludes with a description of two empirical relationships that describe the effect of riprap thickness and cover on the stability of the riprap layer.


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  • Accession Number: 00711545
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 18 1995 12:00AM