Numerical simulation of undrained behavior of granular materials with polygonal particles by discrete element method (DEM)

Document Type : Original Research

Authors
M. Khabazian
E. Seyedi Hosseininia
Ferdowsi University of Mashhad
Abstract
In the present study, discrete element method is used to simulate undrained two-dimensional behavior of soil samples containing polygonal particles. Two methods of constant volume and cylinder were used for numerical simulation of undrained behavior and the results from these two methods were compared. In the cylinder method, it is assumed that there are channels among adjacent pores and the possibility of water exchange among the centers of the pores is provided. In this method, the diameter of the cylinder represents the permeability of the soil. In the constant volume method, it is assumed that the sample volume stays constant during loading. The simulations were done by using both methods. The samples were initially subjected to confining pressure of 200 kPa and after consolidation, they were loaded under deviatoric stress. The results showed that the output obtained by the cylinder method are in good agreement with the constant volume method, and by increasing the stiffness of the water, the results of both methods are closer to each other. Then, the undrained behavior was investigated by using cylinder method in terms of shear strength and pore water pressure in a sand sample at the confining pressures of 200, 400, 800 and 1600 kPa. The trend obtained from the simulation results is in good agreement with laboratory results such that with bigger confining pressure, the shear strength and the positive pore pressure are bigger too, but by increasing confining pressure, the amount of pore pressure decreases in the specimen. The pore pressure distribution contour at the strains of 10% and 30% was presented by means of cylinder method and the effect of cylinder diameter changes on the pore pressure distribution contour was investigated. By investigating the pore pressure distribution contour at the strains of 10% and 30%, it was shown that pore pressure in the sample center has the lowest value. In addition, it was seen that by increasing the cylinder diameter, the variation of pore pressure among the voids becomes smaller, which indicates the uniformity of the pore pressure in permeable soils. By reducing the diameter of the cylinder, the variation of pore pressure becomes more through the sample.

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Modares Civil Engineering journal
Volume 19, Issue 1
May and June 2019
Pages 141-153