Tangential load-deflection behaviour at the contacts of soil particles

This paper describes a laboratory investigation of the response of coarse-grained soil particles at their contacts. The tests were carried out in a newly developed micromechanical inter-particle loading apparatus capable of imposing and measuring loads and deflections at the contacts of non-conforming (i.e. non flat-to-flat) surfaces. The apparatus was designed to investigate the behaviour at contacts over a range of load levels from the initial contact stiffness to failure under sliding. The paper presents tests on a variety of particle contacts, investigating the effects of test conditions as well as particle properties and quantifying the particle roughness using an interferometer microscope. The initial tangential load-deflection behaviour is shown to be highly non-linear and predominantly plastic. The stiffness depends on the normal load applied and the particle type, but does not degrade with small numbers of cycles. Shearing led to a significant decrease in the amplitude of the surface roughness of the particles, mostly through the removal of asperities, which shows that the tangential stiffness might not be significantly affected by the amplitude of surface roughness.