A mechanical model for granular mixtures including particle crushing

Abstract

The ability to model the general stress strain behaviour of granular materials under various shear stress paths, a so-called Markov process, has been well established. The important features of particle breakage and crushing of granular materials under shear stress can easily be introduced into the existing numerical model. Particle crushing plays an important role in the development of stiffness and strength of the material under repeated shear loading. Therfore, the most important question is under which general conditions particle crushing and breakage occurs. The stress level is sought at which crushing starts, and a combination of parameters to describe its occurrence. The relevant relations are analysed by shear tests of a mixture of two kinds of granular particles (φ max = 16 mm), with relatively high (sand, gravel) and low (mortar) individual strength. The tests include various different stress-paths with loading and unloading. In this paper the plastic work transferred into the sample is considered to be essential factor. The increase in content of fines, i.e. the change of the shape of the grain size distribution, is registered for different plastic work done. The linear relationship obtained between plastic work and mean particle diameter (i.e. content of fines) is incorporated into the numerical ‘modified Markov model’ and verified by means of a back calculation for a laboratory shear test.