Mechanism of the progressive failure of non-cohesive natural dam slopes

Progressive failure, which begins in the downstream slopes of dams, is one of the main failure modes for natural dams in the field. However, this failure mode lacks attention in the scientific literature, especially regarding its formation mechanism. In this paper, flume tests were conducted to simulate the progressive failure of a natural dam. The results show that the progressive failure process is induced by seepage water discharging on the downstream slope, including the erosion of individual soil particles, repeated minor slip failures, upward head-cutting erosion of the dam crest, and finally the collapse of the dam when the processes have evolved sufficiently. This study focuses on analyzing the initiation mechanism of soil particle migration. The influence of seepage and interflow stresses on the incipient erosion of soil particles is analyzed. In addition, the buoyancy of soil particles on the downstream slope surface is not considered in the vertical direction in this paper but in the direction perpendicular to the downstream slope surface. The paper also discusses how to estimate the occurrence of the progressive failure of a natural dam. In the estimation method, the stress of the interfacial flow, the seepage flow stress, and the friction stress of the soil particles are considered when the phreatic line reaches the downstream slope surface.