An Investigation of Fines and Coarse Contents in Granular Mixtures by Using Discrete Element Method

Document Type : Research Article


1 Civil Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, Iran

2 Civil Eng. Department, Faculty of engineering, Ferdowsi University of Mashhad


It is believed that the addition of fine-grained soil to a base coarse-grained soil would result in shear strength increment due to filling up the voids among coarse-grained content and reducing global void ratio. However, this belief was against the following experiments. Instead of the definition of classical void ratio, two variables referred to as equivalent inter-granular and inter-fine void ratios, have been proposed to resolve this problem. Using these variables can help how a binary soil behaves. In this paper, by using the discrete element method, several binary soil samples were created by mixing two coarse and fine-grained soils. The two fine and coarse-grained soils have different gradations. The soil samples were prepared by considering zero, 10, 30, 40, 70, 100 percent fines content. Simulations were performed in two-dimension in which, the particles were circular. After each soil sample preparation, it was consolidated under isotropic confining pressure followed by biaxial compression loading. Each sample was tested under three different confining pressures. The biaxial loading condition was continued until the samples reached the critical state. This is the case where there is no variation in the deviatoric stress as well as the volume change along with the increase in the axial strain. Based on the simulated results, the required parameters to estimate the portion of the role of coarse and fine-grained parts in the global soil behavior were obtained. Comparison of the results of this study with those of experiments showed good agreements. The threshold fines content after which, the mechanical behavior of the binary soils is governed by fine grains, was assessed. It was shown that for the two-dimensional samples, the critical state can be obtained and the critical state line (CSL) can be constituted in the q-p’-e space. It was also seen that for the two groups of samples where either of coarse or fine-grained content are dominant, a unique critical state line can be obtained if the inter-granular and inter-fine void ratios are used instead of the global void ratio. The influence factors were back-calculated and the values were justified in comparison with the experiments.


Main Subjects

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