Experimental study of sand grains behavior at their contacts with force- and displacement-controlled sliding tests

Discrete element modeling requires the proper quantification of the behavior of grains at their contacts including the normal force – displacement and tangential force – displacement relationships to be used as input for contact modeling purposes. This paper reports on recent advances in soil mechanics experimentation which allowed measuring the grain contact behavior of small sand particles quantifying friction and stiffness with sliding tests of a force-controlled or displacement-controlled type. The particular focus of this work is on the micromechanical behavior of quartz type grains of size between about 1 and 5 mm. A description of the developed micromechanical apparatus at City University of Hong Kong is first discussed and its important different capabilities with previously developed apparatus is briefly reviewed. Subsequently, a limited set of new data is reported and discussed along with a review of recently acquired results published in the literature associated with the contact behavior of quartz sand grains. These sliding tests have covered a wider range of normal contact forces from about 0.5 to 8 N, and the results indicated that, for this range of confining forces, there is not any notable change of the inter-particle coefficient of friction.