Evolution of the contact network during tilting cycles of a granular pile under gravity

The discrete numerical simulations are performed using the contact dynamics method (Moreau 1994). The grains are perfectly rigid, and interact via frictional contacts governed by a Coulomb friction law (µ= 0.5). The granular pile is made of a two dimensional rectangular box filled with 4000 circular grains of mean diameter D, with a thickness of ≈ 35D, and a width of ≈ 120D. The solicitation consists in quasistatic rotations in the gravity field at a rate of 0.001◦ per time step. Initially, the slope increases from θ = 0◦ to a maximal inclination angle θrev. At that stage, two successive cycles [−θrev; θrev] are performed. All the simulations are averaged over 50 granular piles differing in the initial grains arrangements, and showing characteristic angles θr 15◦ and θa 21◦.