Evolution of Grain-size Distribution of Pumice Sands in 1-D Compression

Crushing is one of the micromechanisms that govern the mechanical behaviour of sands at medium-high stresses. It depends on mineralogy, form and strength of single particle, mean stress level, coordination number, time, etc.. It causes changes of grain-size distribution, porosity, number and type of grain contacts, fabric, structure of the material, etc.. Results of an experimental research on the crushing of pumice sands compressed under 1-D conditions to vertical effective stresses σ′v up to 100MPa are reported here. They show marked crushing already at σ′v of about 200kPa. The evolution of the grain-size distribution can be represented by ΔDi= h/(K(1+C exp(-hlgσ′v))) in which ΔDi is the decrement of the generic characteristic diameter. C, h, K are positive parameters depending on the sand's nature and initial state. This relation properly accounts for the existence of an upper limit to ΔDi (or the existence of a limit grading). It is able also to describe the evolution of the global relative breakage indexes.