Résumé
In order to account for the faceted shapes of ballast grains, we use pentagonal grains in a two-dimensional space. The grains are confined inside a rectangular box with thickness H and length L. The two side walls are free to move horizontally, the base is fixed, and the top wall is subjected to a compressive load or displacement. The numerical sample is composed of approximately 1600 grains: 50% of diameter equal to 2.5 cm, 34% of diameter equal to 3.75 cm, 16% of diameter equal to 5 cm. The coefficient of friction between the grains is µg = 0.6. We used a coefficient of friction µw equal to 0 or 0.6 between the grains and the top and bottom walls.