Discrete numerical modeling of loose soil with spherical particles and interparticle rolling friction

Abstract

Discrete numerical simulations were carried out to reproduce experimental results obtained on loose cohesionless soil samples subjected to triaxial tests. Periodic boundary conditions were adopted and 3D spherical discrete elements were chosen. However, to overcome excessive rolling of such an oversimplified particle's shape, contact rolling resistance was taken into consideration. The influence of both the elastic and the plastic local parameters is discussed. It is shown that the plastic macroscopic behavior of the granular assembly depends only on the plastic parameters at the microscopic scale, and mainly on the plastic rolling moment reflecting the particle's shape. Moreover, a procedure to obtain an initial density, ranging from loose to dense samples, is proposed by adding adhesion at contacts during the preparation phase. Finally, a calibration procedure is proposed to reproduce experimental results and the limitations of the model are discussed.

Numerical Investigation of Caved Rock Mass Friction and Fragmentation Change Influence on Gravity Flow Formation in Sublevel Caving

“…In general, DEM assumes the creation of the models with different element shapes that are subjected to Newton's law of motion and with appropriate constitutive models at their contacts. This method is widely used for the modeling of problems related to granular materials [28][29][30], coal mining [31] and different rock and soil mechanics problems [32][33][34][35][36]. DEM modeling of sublevel caving was demonstrated by Hustrulid, Sellden, DeGagne and Bobadilla [5,[37][38][39][40].…”

Quantitative prediction of discrete element models on complex loading paths

“…If the elastic parameters are chosen sufficiently close to the rigid limit, then the plastic properties of the granular assembly at the macroscopic scale depend on the contact plastic parameters ( η r and φ c ) only, and the macroscopic elastic properties are fixed by the elastic contact properties ( E c , α t ). The choice of the mechanical parameters has been performed in accordance with this condition by following the calibration methodology defined by Aboul Hosn et al Only a brief recall about this methodology is given here. •The first step consists in calibrating η r to fit the shear strength at large deformation (at critical state), which depends only on η r (if φ c is not too low).…”

“…The choice of the mechanical parameters has been performed in accordance with this condition by following the calibration methodology defined by Aboul Hosn et al Only a brief recall about this methodology is given here. •The first step consists in calibrating η r to fit the shear strength at large deformation (at critical state), which depends only on η r (if φ c is not too low). In this objective, a cloud of nonoverlapping particles is isotropically compacted until reaching the target confining pressure.…”

“…The latter is done by choosing a contact friction for compaction lower than the nominal contact friction angle used to simulate the mechanical test. Further information concerning the initial compaction of numerical granular assemblies via an isotropic compaction can be found for instance in the works of Combe and Roux or Aboul Hosn et al •In the third step, the nominal value of the contact friction angle is calibrated (if necessary) to improve the reproduction of the volumetric deformation and the peak shear strength. •Finally, in the fourth step, the contact stiffness modulus E c and the tangential coefficient α t are adjusted to improve, if necessary, the reproduction of the slopes at low deformation of the macroscopic stress‐strain response and of the volume variation, respectively (see for instance the plots of σ 1 / σ 3 vs ε 1 and Δ V / V vs ε 1 in Figure ), reflecting partly the elastic properties of the soil sample.…”

“…Consequently, the model fails to describe accurately the change of mobilized friction angle with mean pressure. As discussed in Aboul Hosn et al, it may be related to the Coulombian friction model (Equation ) where the contact friction angle is independent of the normal contact force, which is of course consistent with the Coulombian model but may not be totally true (more likely for high confining pressure and easily degradable grains).…”