Tangential contact behaviour of a weathered volcanic landslide material from Hong Kong

This study reports on the inter-particle coefficient of friction and tangential stiffness at the contacts of completely decomposed volcanic (CDV) granules taken from a landslide in Hong Kong. Micromechanical sliding experiments were conducted using a new generation inter-particle loading apparatus on pairs of granules of about 1.18–2.36 mm in size in a quasi-dry state to explore their tangential load – displacement behaviour. For this purpose, small shearing paths were applied in monotonic mode under nominal normal loads in the range of 0.5–1.0 N. The results demonstrated that the inter-particle coefficient of friction was much higher and the tangential stiffness was much lower than reported values in the literature for quartz sand grain contacts. Repeating shearing tests following the same shearing path showed a notable change of the tangential force – displacement relationship from the first to the second cycle, while subsequent cycles had a relatively small effect. Scanning electron microscope (SEM) images revealed some damage to the surface of the granules on the meso-scale, but no effect on the structure of the grains at the micro-scale was observed. It is believed that the soft nature of the grains and their high surface roughness may have contributed to these trends.