Experimental study on the process of overtopping breach of concrete-faced sand-gravel dam

Abstract

A concrete-faced sand-gravel dam (CFSGD) is likely to experience a dam breaching accident once there is leakage through the concrete face slab joints or overtopping of the dam. This study aimed to examine the physical process of a CFSGD overtopping breach and considered the influence of the failure of the vertical joint water barrier. The similarity criterion of the model test was deduced and the face slab that met the requirements of the model test was prepared. Through flume model tests, the process of overtopping dam breach was divided into four stages, i.e. Stage I, seepage erosion stage, Stage II, gradual erosion stage, Stage III, violent dam breach stage and Stage IV gradual stabilisation stage. The results showed that under the influence of seepage erosion, the initial breach of the dam occurred at the upper edge of the seepage surface of the downstream slope. The flow process line of the breach was of a ‘lean and high’ type, and there was a clear increase in the average rate of undercutting and horizontal expansion of the breach, highlighting the important influence of the early seepage erosion stage on the later dam breach process.