Influence of Seepage Length on Backward Erosion Piping Behaviors in Centrifuge Model Testing

A series of centrifuge tests were performed to evaluate the backward erosion piping behavior that occurred in models with the same soil and same dimensions and to investigate the influence of the seepage length, exit-hole size, and gravitational acceleration. Pore-pressure measurements at various locations within the model, along with video recordings, were used to analyze the models. The mechanism began with seepage across the model, followed by emerging seepage, which changed the flow direction toward the exit hole. The mechanism developed steadily for models with shorter seepage lengths, allowing identifying soil loosening, the initiation of erosion, and failure. In comparison, the mechanism developed rapidly in models with longer seepage lengths, without a clear progression. The values of critical hydraulic gradients across the upstream and downstream reservoirs, the seepage length of the models, and near the exit holes were similar, regardless of the seepage length. The critical hydraulic gradients decreased as the gravitational acceleration increased, indicating some scaling effects. Regardless, the overall effect of centrifuge gravity on the critical hydraulic gradients was small compared with the range of values that have been reported in the literature.