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 geometry and different surface roughness on the measured wall friction coefficients of binary granular mixtures. Shear cell tests carried out with mono-size beds of coarse particles (d > 1 mm) under different types of packing configurations were repeated after the addition of the maximum possible amount of fine material into the packing at different particle size ratios. Similar experiments were also performed with mixtures of particles of smooth and rough surfaces. The relationship between the wall friction coefficient and the compressive stress tends to be strongly affected by the surface roughness of the constituent particles. The wall friction coefficient of an assembly of smooth particles is altered significantly by the addition of rough particles of similar size but of lower coefficient of friction, while rough particles 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 assembly frictional behaviour is found to be dominated by the fines. (C) 1999 Elsevier Science Ltd. All rights reserved.