Parametric study of riprap failure around bridge piers

Abstract

This paper presents a parametric study on riprap protection around a cylindrical bridge pier with uniform bed sediments. Riprap layers with different characteristic parameters: thickness, cover width, and placement level of the riprap layer; median grain size and density of the riprap stone; and undisturbed approach flow depth were tested under a sequence formation of ripples, dunes and transition flat bed. Observations show that a riprap layer will eventually degrade to a maximum level which is the same as the maximum pier scour depth when the riprap layer is not present. This study proposed a criterion to determine the maximum embedment level and the embedment velocity, i.e., the flow velocity at which the riprap layer has embedded to its maximum level. The experimental results show that variations of the characteristic parameters have no influence on the embedment failure at the upper end of the dune regime. The study also proposes a maximum embedment velocity, which defines a critical flow velocity at which all riprap layers, irrespective of the characteristic parameters will fail.