An experimental investigation of work dissipation in crushable materials

Abstract

Using simple direct shear tests on a carbonate sand, an experimental validation has been provided for the Taylor work dissipation equation, modified to include a term for particle breakage. The shear tests have been carried out on monogranular and fractal grain size distributions of a crushable carbonate sand at vertical stresses ranging from 200 kPa to 1400 kPa and horizontal displacements from 0·5 mm to 8 mm. In order to compare particle breakage of specimens with different particle sizes, specimens were prepared with a sample height of about 20d50. Grain size distributions were measured before and after shearing. A link has been established between grain crushing, shear strength and general mechanical behaviour of sands. In particular, an explanation has been given for the phenomenon of the curvature of the Mohr–Coulomb envelope observed at apparent ultimate conditions in sands using measurable physical variables related to particle crushing. The apparent critical state friction angle has been shown to contain both frictional and clastic components. Examination of these separate components of shear resistance leads to the conclusion that the apparent critical state angle of friction increases as the rate of particle crushing, normalised with respect to the normal force, increases. It was also observed that the normalised rate of crushing levelled off as a stable fractal dimension for the grain size distribution was achieved.