Parametric study of riprap failure around bridge piers

This paper presents a parametric study on riprap protection around a cylind rical bridge pier with uniform bed sediments. Riprap layers with different characteristic parameters: thickness, cover width, and placement level of t he riprap layer; median grain size and density of the riprap stone; and und isturbed approach flow depth were tested under a sequence formation of ripp les, dunes and transition Rat bed. Observations show that a riprap layer wi ll eventually degrade to a maximum level which is the same as the maximum p ier scour depth when the riprap layer is not present. This study proposed a criterion to determine the maximum embedment level and the embedment veloc ity, i.e., the flow velocity at which the riprap layer has embedded to its maximum level. The experimental results show that variations of the charact eristic parameters have no influence on the embedment failure at the upper end of the dune regime. The study also proposes a maximum embedment velocit y, which defines a critical how velocity at which all riprap layers, irresp ective of the characteristic parameters will fail.