A Hydromechanical Concept for the Triggering of Internal Erosion in Widely-Graded Soil

Abstract Internal erosion manifests as particle loss at the micro-pore scale in a soil matrix, else as particle loss at the macro-pore scale in cracks, fractures, pipes, and fissures. Risk management of internal erosion in dam safety engineering is, at the time of writing, entirely based on empirical screening methods. Empirical methods have no explanatory power, and this BC Hydro-NSERC funded research identifies the governing mechanics at the micro-pore scale in widely-graded cohesionless soil. Analysis of flexible-wall permeameter data on a sand-gravel test specimen, reconstituted from borrow pit material for the WAC Bennett Dam in Canada, establishes a novel relation in stress-gradient space for the initiation or triggering of internal instability in a susceptible gradation. The experimental relation appears consistent with the theoretical concept of a stress-reduction factor acting on the finer fraction content of a potentially unstable widely-graded soil.