Multiple contact compression tests on sand particles

Particle crushing has been recognised to be of key importance for many engineering applications. In soil mechanics, this phenomenon has become crucial in defining a complete framework able to describe the mechanical behaviour of sands. In this study, the effect of multiple discrete contacts on the breakage of a grain was investigated, crushing coarse grains of a quartz sand and a crushed limestone sand between a number of support particles, thereby varying the number of contacts, i.e. the coordination number. The stress at failure was calculated when the particle broke, which was through a number of distinct modes, by chipping, splitting or fragmenting which were observed with the use of high speed microscope camera. The Weibull criterion was applied to calculate the probability of surviving grain crushing and the fracture modes were observed for each configuration of the supporting particles. The data showed that in addition to the number of the contacts the nature of those contacts, controlled by the particle morphology and mineralogy, play a significant role in determining the strength of a particle. The sphericity affected the strength for the softer limestone while the local roundness at the contacts was important for the harder quartz sand. Catastrophic explosive failure was more often observed in particles with harder contacts while softer contacts tended to mould relative to their neighbouring particles inducing a more frequent ductile mode of crushing.