Coefficient of friction of binary granular mixtures in contact with a smooth wall PART I: Direct shear bore measurements of the effects of particle size ratio and particle surface roughness

The effects were investigated of the varying fine fractions, packing geomet ry and different surface roughness on the measured wall friction coefficien ts of binary granular mixtures. Shear cell tests carried out with mono-size beds of coarse particles (d > 1 mm) under different types of packing confi gurations were repeated after the addition of the maximum possible amount o f fine material into the packing at different particle size ratios. Similar experiments were also performed with mixtures of particles of smooth and r ough surfaces. The relationship between the wall friction coefficient and t he compressive stress tends to be strongly affected by the surface roughnes s of the constituent particles. The wall friction coefficient of an assembl y of smooth particles is altered significantly by the addition of rough par ticles of similar size but of lower coefficient of friction, while rough pa rticles of finer size appear to have far less effect. In contrast, when the fines are smooth particles and the coarse particles are rough, then the as sembly frictional behaviour is found to be dominated by the fines. (C) 1999 Elsevier Science Ltd. All rights reserved.