Experimental investigation into embankment external suffusion

External suffusion, as selective erosion of fine particles through the contact with a coarser layer and moving away, is an important phenomenon in dams which may lead to their failure. To study the initiation of external suffusion, caused by water level increase upstream the dam, a series of experimental investigations were conducted on laboratory-scale model, in the hydrodynamic laboratory of École polytechnique de Montreal. On the built model, clay/moraine formed the core, sand was used as a filter and gravel performed the role of the pervious layer. Several different models (in geometry and constituent materials) were built and subjected to the water level increase upstream, which resulted in changes in the hydraulic gradient. The results showed no evidence of considerable suffusion on the clay/moraine and sand interface, while the visual and quantitative data show the presence of suffusion on the sand and gravel interface. The results of the experiments show that, when focusing on the critical hydraulic gradient that initiates the movement of the clay/moraine particles, it can be concluded that despite the differences in test conditions, the critical hydraulic gradient has approximately the same value in all cases. It was also shown that increasing the length of the filter layer or applying stair-like slopes does not have great impacts on the initiation of suffusion, whereas the gravel-size distribution has a great impact on the erosion rate. Copyright Springer Science+Business Media B.V. 2010