This paper presents a study of the micromechanical behaviour of crushable soils, For a single grain loaded diametrically between flat platens, data are presented for the tensile strengths of particles of different size and mineralogy, These data are shown to be consistent with Weibull statistics of brittle fracture, Triaxial tests on different soils of equal relative density show that the dilatational component of internal angle of friction reduces logarithmically with mean effective stress normalized by grain tensile strength. The tensile strength of grains is also shown to govern normal compression, For a sample of uniform grains under uniaxial compression, the yield stress is related to the average grain tensile strength. If particles fracture such that the smallest particles are in geometrically self-similar configurations under increasing macroscopic stress, with a constant probability of fracture, a fractal geometry evolves with the successive fracture of the smallest grains, in agreement with the available data. A new work equation predicts that the evolution of a fractal geometry gives rise to a linear compression line when voids ratio is plotted against the logarithm of macroscopic stress, in agreement with published data.
