MOTION OF CONTACT-LOAD PARTICLES AT HIGH SHEAR-STRESS

For rivers in flood and beaches under wave attack, the shear stress at the top of the stationary granular bed can set up a sheared layer of contact-load (bed-load) particles. This type of motion also occurs in pressurized conduits, where more accurate observations can be obtained. For high shear stress (Y > 0.8) the shear layer has a thickness of several grain diameters. Experimentation and analysis demonstrated that mobile beds at high shear stress obey neither the smooth-boundary nor the rough-boundary law, but follow a different friction relation of their own, which does not depend on particle size. This analysis has now been significantly extended using a curvilinear concentration profile based on previous experiments. This profile is now applied to the evaluation of boundary friction and the transport rate of contact-load solids. The present analysis provides the theoretical background to explain both existing experimental results and new data presented here.