A study of the effect of particle size on mechanical behavior of granular materials is reported

by conducting a series of direct shear tests on a special granular material-glass bead. In this investigation

three approximately parallel grading curves are taken into consideration; and also four types of inter-particle friction conditions are concerned

including dry state

water-lubricated state

flooded state and oil-lubricated state. The test results indicate that particle size exerts a pronounced effect on mechanical behaviors of granular materials and that dilatancy is enhanced with the increase of particle size. On the basis of test results

a stress-dilatancy relationship is brought forward to appropriately take into account the effect of particle size on the dilatancy of granular materials. The dilatancy coefficient in this proposed relationship is revealed to be a variable dependent on particle size

inter-particle friction and other basic particle attributes. In the meantime the critical state friction angle is found to increase with the increasing particle size. In addition

an energy-work model of particle sliding behavior is proposed from a perspective of mesoscopic particle motions. Based on this proposed model

the energy-work equation is derived and the essential mesoscopic mechanisms underlying the effect of particle size on critical state friction angle are accordingly elaborated.