Prediction of the Hydraulic Gradient for Backward Erosion Piping in River Levees

The hydraulic gradient that causes backward erosion piping of river levees is a matter of significant concern in geotechnical engineering. As the pipe progresses due to pipe wall erosion and bedload transport, it has been recognized that pipe geometry and flow regime significantly influence pipe progression. This paper described a new prediction method that considers the effects of foundation soil properties, levee scale, flow regime, and pipe geometry. The method was validated by comparing the predicted results with those of the centrifuge test results. It was confirmed that all the analysis results were consistent with those of the test observations. The proposed method satisfactorily predicted the effects of testing parameters in centrifuge experiments on the hydraulic gradient of pipe progression. Finally, the progression gradient of prototype-scale levees was analyzed using the proposed method. The gradient was confirmed to be inversely proportional to the square root of the levee width L−1/2 under the laminar pipe flow condition, whereas the exponent may be even smaller under the turbulent flow condition, which is more likely to be observed in field-scale levees.