Combined Geometric Hydraulic Criteria Approach for Piping and Internal Erosion in Cohesionless Soils

Abstract

Abstract Piping is an erosion mechanism that plays a significant role in river barrages, such as dikes and dams, that are founded on poorly graded cohesionless soils like, for instance, fine or medium sands. Likewise, in gap-graded or widely graded cohesionless soil, finer grains can pass through the pore matrix of coarse soil because of seepage. This phenomenon, which is called internal instability or suffusion, can occur in granular filter in or under dams, dikes, barrages, or any other water-retaining structure. For economic reasons, unstable soils are generally used in practice if the hydraulic force or the hydrodynamic energy is smaller than the critical hydraulic force or the critical hydrodynamic energy. Therefore, an approach of combined geometric-hydraulic criterion is expected to yield better results. Based on this premise, laboratory tests of piping and internal erosion are carried out using five cohesionless soils. An analysis of the results considering the instability index shows that the critical hydraulic gradient required to initiate the piping and internal erosion depends on the curve of the grain size distribution, the initial relative density of the soil, the seepage direction, and the initial stress condition in the soil. Based on these laboratory results and the results reported by several other authors, a combined geometric-hydraulic criterion with respect to piping and internal erosion in cohesionless soils is developed and proposed.