Fundamentals and Theory of Air Scour

Abstract

An original theoretical analysis of the dynamics of air scour from a fundamental and microscopic viewpoint is presented. Concepts in soil mechanics and porous media hydraulics are combined to explain the complex flow patterns which emerge when air and water flow concurrently through porous media. An equation which predicts the formation and collapse of air pockets within the bed is developed by equating the air pressure within a bubble to the soil stresses in an active Rankine state plus the pore‐water pressures. This condition of collapse‐pulsing which occurs at particular combinations of simultaneous air and subfluidization water flows has been associated with the probable optimum condition for air scour. The theory compares well with four sets of experimental data collected on two different graded sands. The theoretical expression has been condensed into a simple design equation for practical application.