Backward Erosion Piping: Influence ofFull Grain Size Distribution

Abstract

Backward erosion piping is a significant erosion mechanism that jeopardizes safety of dams by forming a continuous pipe in the foundation. The progression of erosion has historically been evaluated by considering the erosive force of seepage flow and the resistance of the soil material. This resistance is well understood for uniform materials; however, further research is required for more widely graded soils to account for the influence of the entire grain size distribution in characterizing the erosion process. This study investigates the influence of the full grain size distribution, focusing on the influence of different grain size ratios, such as d 90 / d 10 , material coarseness, and fines content on the incipient motion of particles. Experimental results on silty sand to medium sand indicated a relationship between the d 90 / d 10 ratio and the critical global gradient, with soils having a higher d 90 / d 10 ratio requiring a higher critical hydraulic gradient, regardless of material relative coarseness. Moreover, in nearly uniform fine-grained soils with a low d 90 / d 10 ratio, finer particles mobilized first, resulting in a lower representative grain diameter governing the erosion process.