Micromechanical experiments using a new inter-granule loading apparatus for gravel to ballast-sized materials

Micromechanical and tribological studies of geological materials with a particular focus on theircontact-mechanics behavior at the grain scale are currently a major interest in the engineering and geosciencedisciplines. In this study, a new robust micromechanical apparatus developed at the City University of HongKong is described; it is capable of conducting inter-granule (or inter-particle) loading tests on fine gravel toballast-sized materials of sizes as small as 5−10 mm to granules (or ballast) as big as 50 mm. The focus of ourstudy is the description of the major technical features of the new apparatus and its performance andrepeatability in conducting experiments on reference grains of chrome steel balls and glass balls; in addition,we conducted a preliminary set of experiments on crushed granitic rock, which is a material widely used ingeotechnical and transportation infrastructure. The representative results of these experiments are presented interms of the normal force-displacement relationship, friction, and tangential stiffness. The newly developedlarge-size apparatus is further compared with a well-established apparatus that can conduct micromechanicaltests on sand-sized materials.