On the micromechanics of crushable aggregates

Abstract

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 geotoscopic 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 geotoscopic stress, in agreement with published data. Cet exposé présente une étude du comportement micro mécanique des sols concassables. Pour un seul grain chargé de manière diamétrale entre des platines plates, nous présentons les données de résistance à la rupture des particules de différentes dimensions et minéralogies. Nous montrons que ces données correspondent aux statistiques de Weibull sur la rupture de fragilité. Les essais triaxiaux sur divers sols de meême densité relative montrent que le composant de dilatation de ľangle interne de friction baisse de manière logarithmique en mê"me temps que la contrainte effective moyenne normalisée par la r6sistance à la rupture du grain. Nous montrons aussi que la résistance à la rupture des grains gouverne la compression normale. Pour un échantillon de grains uniformes sous compression uniaxiale, la limite 61astique est liée à la rupture moyenne des grains. Si la rupture des particules est telle que les plus petites particules sont dans des configurations à similitude géomé trique intrinsèque sous un effort geotoscopique de plus en plus grand, avec probabilité constante de rupture, une géométrie fractale apparaît avec la rupture successive des grains les plus fins, en accord avec les données disponibles. Une nouvelle équation de travail prédit que ľévolution de la géometrie fractale provoqueľPapparition ďune ligne de compression linéaire quand le taux de pores est représenté sous forme de courbe par rapport au logarithme de ľeffort geotoscopique, en accord avec les données pub-liées.

Breakage of an artificial crushable material under loading

“…This conflicts with the growing understanding that the grain size distribution of aggregates of any initial grading, under extremely large confining pressure and extensive shear strain, tends to a self-similar, fractal distribution [25,37].…”

“…A number of recent detailed studies have considered the relationship between particle crushing and soil mechanical behaviour ( [1,[3][4][5]4,7,9,23,25,28,36]). From the point of view of constitutive modelling, the question to be addressed is how microscopic degradation phenomena, such as grain crushing, affect the macroscopic properties of a granular aggregate, ideally deducing macroscopic constitutive equations from micromechanical consideration of some underlying microscopic process [25].…”

“…From the point of view of constitutive modelling, the question to be addressed is how microscopic degradation phenomena, such as grain crushing, affect the macroscopic properties of a granular aggregate, ideally deducing macroscopic constitutive equations from micromechanical consideration of some underlying microscopic process [25]. Quite recently, the idea of a fractal evolution of particle size has been adopted introducing a breakage parameter into energy dissipation assumptions of a crushable soil treated as a continuum [8], and through links between particle crushing and critical states in soils [33,43].…”

Failure behavior of single sand grains: Theory versus experiment

“…The former are in accordance with our measurements on single sand grains of different grain size. The (extent of the) discrepancy between the expected and the measured grain size dependencies is attributed to the internal microstructure of the grains [Tsoungui et al, 1999], such as intraparticle porosity [McDowell and Bolton, 1998] and flaw distribution, as this is reflected in the Weibull modulus m.…”

Mechanical properties of lightweight aggregates

“…Investigations on mechanical strength of irregular shaped soil particles were amongst other carried out by McDowell et al [43][44][45] and Dexter and Kroesbergen [29]. These studies reviewed again several other works that were assessing the strength of irregular shaped particles.…”