Abstract
This paper aims at investigating the influence of grading on the undrained behavior of granular materials. Series of undrained triaxial tests were carried out with two different materials, glass balls and Hostun sand. For each material, samples with different gradings and similar relative densities were prepared. Experimental results show that the undrained shear strength decreases when the coefficient of uniformity Cu=d60/d10 increases from 1.1 to 20. The conditions of instability for the selected granular materials were also analyzed, based on the sign of the second-order work during undrained triaxial loading. The results demonstrate a significant influence of the grading: increasing the coefficient of uniformity heightens the potential of static liquefaction and the materials become more unstable. Furthermore, numerical tests using the three-dimensional discrete element method (DEM) were conducted on assemblies of spheres. The DEM inter-particle parameters were derived from the experimental test results on glass balls. The DEM simulations showed similar behaviors compared to experimental results and confirmed the influence of the grain size distribution on the stress–strain relationship and instability phenomena.
Highlights
Certain mechanical characteristics of granular materials under undrained condition, such as shear strength and instability, are of great importance in geotechnical engineering
Series of undrained triaxial tests on different materials (Hostun sand, glass balls, and idealized sphere packing by discrete elements method (DEM)) were carried out, for each material on samples with different gradings but similar relative density, in order to investigate the grading effect on the undrained behavior of granular materials
For samples with the same relative density, the undrained shear strength and the phase transformation deviatoric stress gradually decrease with the increasing coefficient of uniformity Cu, and tend to stabilize for Cu higher than 10
Summary
Certain mechanical characteristics of granular materials under undrained condition, such as shear strength and instability, are of great importance in geotechnical engineering. It is generally accepted that the second-order work theory postulated by Hill [16,17] can be used as a stability criterion, the material being potentially unstable if the sign of the second order work becomes negative at a given mechanical state. If this condition is reached, it does not always imply that failure would occur, as experimentally demonstrated by Lade and Pradel [18]. Evaluating the grading influence on undrained behavior of granular materials is the main focus of this study. Numerical triaxial tests by means of the three-dimensional discrete elements method (DEM) were carried out on spheres assemblies with different gradings in order to complement the experimental results
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