Hydraulic loading in culvert inlets

Flexible corrugated metal pipes are commonly used as an alternative to concrete bridges for small and medium sized streams. If these flexible culverts are improperly designed they can fail dramatically. One cause of failure is uplift at a submerged inlet. With the pipe flowing partly full, the weight of the pipe and the net force due to the internal water pressure may be less than the buoyant force acting on the submerged pipe; this may result in an upward bending moment. This paper describes an experimental study of the hydraulic forces inside culvert inlets. The tests were carried out on a plexiglass pipe with projecting and flush inlets. The effect of the flow separation on the pressure fluctuation at the inlet was investigated in this study. The internal pressures for the case with a headwall were found to be significantly higher than for the projecting inlet. The formation of a scour hole at the upstream end of the inlet increased the uplift potential. Internal pressure profiles were integrated to determine the internal load distributions on culverts with different inlet treatments.