Piping failure is among the most common failure modes for embankment dams. It is often related to the potential of the embankment material to de-flocculate and erode in the presence of water. Soil erosion is therefore one of the main factors affecting the safety and serviceability of earth structures. This paper presents the results of a laboratory testing program intended to study the effects of dry density, moisture content and curing time on the erodibility and dispersivity of two alluvial deposits aimed to be used as dam core material. One sample is a recent deposit obtained from the flood plains of the River Nile in Northern Sudan (Soil A) while the other (Soil B) is obtained from an adjacent area in the upper terraces of the Nile. Preliminary evaluation has shown that Soil A is slightly dispersive while Soil B is highly dispersive.

Specimens from the two samples were prepared in the laboratory at different moisture and density conditions and tested for dispersivity and erodibility using the pinhole test. Identical specimens were prepared, cured for different periods of time extending up to 18 months and tested. The results have shown that the erosion resistance of the slightly dispersive Soil A improved with increase in dry density when the moisture content is wet of optimum and with curing time for specimens with lower density and moisture content. However, the highly dispersive Soil B did not show significant improvement of its erosion resistance, neither with increase of its density nor with increase in curing time.