Pier and Abutment Scour Interaction

This paper presents the results of a series of flume experiments to evaluate the interactions between pier-scour and abutment-scour in a noncohesive boundary. To facilitate optimal structural design and minimize pier presence in a channel, many bridges have a pier located close to an abutment. Scant information exists as to how bridge pier proximity to abutment affects scour depth at an abutment and at a pier. The existing relationships for predicting scour at a pier or at an abutment in isolation do not estimate scour depth at a pier or an abutment when both are in close proximity to one another. During this study, scour depth, scour location, and bathymetry data were recorded for two common abutment forms: spill-through and wing-wall. For the abutment and pier configurations investigated, the results show that pier presence does not lead to substantial increases in abutment scour depth, although it may reduce abutment-scour depth when the pier is close to the spill-slope toe of a spill-through abutment; the pier acts to retain riprap stone and spill-slope soil in the scour region. However, scour depth at a pier located close to an abutment is determined predominantly by scour at the abutment and, therefore, may substantially exceed the depth estimated for an isolated pier.