A micromechanical experimental study of highly/completely decomposed tuff granules

In this paper, an experimental micromechanical study is presented investigating the contact mechanics and tribological behaviour of highly/completely decomposed tuff granules. The parent material was taken from two locations—named the top and bottom—from a recent landslide in Hong Kong, and in this study the tested granules were obtained from the parent material after drying and sieving processes. Basic material characterisation was conducted quantifying the particle shape, the surface roughness and the strength of a set of grains. A set of twenty-nine monotonic inter-particle shearing tests were conducted on pairs of granules taken from the top and bottom of the landslide. It was found that the granules had very high friction angles at their contacts, in general greater in comparison with other materials reported in the literature. The slightly greater inter-particle friction for the granules taken from the top of the landslide might be because of their higher roughness in comparison with the ones from the bottom. Additional experiments were conducted to investigate the normal and tangential load–displacement response of the granules subjected to cyclic loading. A good curve fitting for the normal load–displacement response could be obtained by using very low apparent Young’s moduli in the Hertzian model. In general, the decomposed tuff granules showed significant plastic response during the first normal load cycle, and this plastic behaviour continued for the subsequent third and fourth cycles. In the cyclic inter-particle shearing tests, the nonlinearity and hysteresis increased for larger cyclic displacements, but the effect of the number of shearing cycles on the energy loss was generally small. Finally, a limited discussion is presented on the applicability of a theoretical model on the tangential load–displacement behaviour of the granules.