Riprap

Abstract: The objective of this study is to review existing methods and propose alternative or additional devices for scour protection around bridge piers. Engineering methods used in dealing with pier‐scour problems include placing coarse riprap around the foundations. An inverted filter layer is normally placed beneath the riprap to overcome leaching problems. Practical difficulties in laying the filter according to specifications, especially in deep water, often cause failure of the riprap layer. The study examines the effect of using a slot in the pier, or a collar around it, as devices for controlling the depth of scour. Experiments conducted in clear‐water conditions show that the use of a slot alone (with a width equal to one‐fourth of the pier diameter) can reduce equilibrium scour depth by as much as 20%. A combination of slot and collar can further reduce the scour depth. These devices may be useful as additional or alternative devices for scour protection.

Abstract: Engineering methods to deal with pier-scour problems include placing coarse riprap stones around the bridge pier. This study aims to investigate the stability of a riprap layer around a cylindrical bridge pier. Experiments conducted in a laboratory flume identified three different modes of riprap failure. They can act singly or combine to render a complete failure of the riprap layer. These modes of failure are riprap shear failure, winnowing failure, and edge failure. The study proposes a semiempirical method to size stones for riprap protection. The procedure for this method was illustrated with field data from three different bridge sites. The experimental data show that a thick riprap layer can prevent winnowing in the absence of a filter layer. The thick riprap layer can also sustain a partial breakup of the layer with the capability of rearmoring the scour hole, preventing a total disintegration of the riprap layer. Finally, the study proposes two empirical relationships, which describe the effect of riprap thickness and cover on the stability of the riprap layer.

Abstract: Although riprap is the most commonly employed countermeasure against scouring around bridge piers, few studies exist of riprap performance under live-bed conditions. In this study, failure mechanis...

Abstract: Tests to determine stability characteristics of various armor-unit shapes; new stability formula for rubble breakwaters was derived, which provides essential information for improved design; stability, thickness, and porosity data are presented for quarry-stone and tetrapod armor units.