By experiments described in his 1954 paper, Bagnold showed that when a shear flow is applied to the suspension, then the shear and normal stresses in the suspension may vary linearly or quadratically with the shear rate, depending on the strength of viscous effects compared to the particles' inertia.
If the shear and normal stresses in the mixture (suspension: mixture of solid and fluid) vary quadratically with the shear rate, the flow is said to satisfy Bagnold’s grain-inertia flow. If this relation is linear, then the motion is said to satisfy Bagnold’s macro-viscous flow.
These relationships, particularly the quadratic relationship, are referred to as the Bagnold rheology. 
Although Bagnold used wax spheres suspended in a glycerin-water-alcohol mixture, many subsequent shear-cell experiments for both wet and dry mixtures, as well as computer simulations, have confirmed these relations.
 Bagnold's rheology can be used to describe debris and granular flows down inclined slopes.