The Effect of Dilation and Particle Breakage on the Volumetric Behavior of Carbonate Sands (Technical Note)

In this paper the volumetric behavior of four carbonate sands having different physical properties and crushable grains are investigated using isotropically consolidated-drained triaxial tests. Three sands were obtained from the north shores of the Persian Gulf, south of Iran, called Hormoz, Kish and Tonbak sands, and one was obtained from the south beaches of England and called Rock beach sand. The studied sands have different particle size distribution, shapes and physical properties. Shapes of the grains in these soils are as platy, needle, bulky, angular, subangular and porous, in which show the different sources and deposition environments of them. Tests results conducted on the studied carbonate sands show that different properties of them result in different particle breakage ratio during loading, so that it increases with confining pressure, axial strain, slenderness and area to thickness ratio of the soil grains. Volumetric response of these soils is complex due to interaction of dilation and contraction resulted from particle breakage during shear loading. Therefore, regarding the unknown values of void ratios changes from dilation and particle breakage, the critical state concept become complex. In fact, there is not a real critical state in these soils at least up to axial strain of %20. It is also impossible to reach the critical sate concept using the common triaxial tests apparatus considering of its axial strain limitation. The randomly observed deformation under constant volume is apparent and not real. Such a situation is the volumetric balance between dilation and contraction due to particle breakage. Considering the relative values of these two parameters, the location of the apparently critical state is variable and curve shape, and it is depend on the initial void ratio, dilation, particle breakage and confining pressure. It is expected that the dilation ends up fast, however, particle breakage occurs as the shear strains are applied.