Experimental study on the failure of a dike foundation caused by backward erosion piping under gradual and sudden hydraulic loads

Backward erosion piping (BEP) is a common type of internal erosion that is an important cause of dike failure. To date, research on BEP has been mainly carried out under the action of a gradually increasing hydraulic load, which does not fully represent the actual engineering situation. In this work, the effects of gradually increasing and suddenly applied hydraulic loads on the BEP of double-layer dike foundation are comprehensively studied through laboratory tests. The influences of the exit hole diameter and different types of hydraulic loads on BEP were quantitatively analyzed in terms of the morphological characteristics of the erosion channel, particle loss amount, flow rate of the exit hole and average development speed of the erosion channel. The results show that the occurrence and development process of BEP can be divided into four phases: stabilization, soil expansion, particle erosion and reverse erosion. With the increase of the diameter D of the exit hole, the critical hydraulic gradient i_cr increases, but the local critical hydraulic gradient i_5cm-cr near the exit hole decreases. Compared with that under gradual hydraulic loading, the degree of erosion of a sample under sudden hydraulic loading is higher. The erosion channel depth and width, particle loss rate and exit hole flow rate increase with increasing exit hole diameter D, subcritical coefficient λ and sudden load coefficient µ. The average development rate of the erosion channel increases with larger values of the subcritical coefficient λ and the sudden load coefficient µ, and with smaller values of the exit hole diameter D.