Centrifuge modeling of scale effect on hydraulic gradient of backward erosion piping in uniform aquifer under river levees

Abstract

The hydraulic gradient that causes backward erosion piping under a river levee is influenced by the scale of the levee, which is a major concern in the physical modeling. In this study, the results of 1 g and centrifuge tests performed on backward erosion piping were analyzed to facilitate a better understanding of the scale effect mechanism. The three-dimensional profile of the pipe and the flow rate of water in the pipe were observed using a transparent model levee. Although the flow in the pipe was determined to be laminar in most tests, it was found to be transient and turbulent in the coarse sand model at high g levels. The hydraulic gradient in the pipe was significantly high in the turbulent flow. Additionally, the scale effect was investigated based on the hydraulic conditions that cause sand transportation in an ideal pipe. The critical Shields number (θc), estimated for the model pipes, was consistent with that observed in the Shields diagram. The effects of centrifugal acceleration on the hydraulic gradient of the extending pipes can be explained by the change in θc with the particle Reynolds number and the hydraulic gradient in the pipe.

Keywords

• Backward erosion piping
• River levee
• Centrifuge test
• Shields number