Predicting possible leakage due to dynamics strain localization in granular materials with a coupled continuum-discrete coupling model

A three-dimensional multiscale model has been developed and used to analyze the evolutions of microstructural attributes and hydraulic properties inside dilatant shear bands. In the proposed multiscale coupled scheme, we establish links between the discrete element method, which explicitly replicates granular motion of individual particles, and a fi nite element continuum model, which captures the homogenized responses of the granular assemblies. A spatial homogenization is performed to obtain the stress measure from representative elementary volume of discrete element simulations for macroscopic explicit dynamics fi nite element simulations. We demonstrate that the multiscale coupling scheme is able to capture the plastic dilatancy and pressure-sensitive frictional responses commonly observed inside dilatant shear bands and replicate the induced anisotropy of the elasto-plastic responses, without employing any phenomenological plasticity model at macroscopic level. To improve cost-effi ciency and prevent shear locking, a one-point quadrature rule is used along with an hour-glass control algorithm. Because discrete element simulations in each representatively elementary volume (Gauss point) requires no direct communication with its neighbors, the multiscale code can be programmed as a perfectly parallel problem, which is well suited to large scale distributed platforms and does not suffer parallel slowdown. The resultant multiscale continuum-discrete coupling method retains the simplicity and effi ciency of a continuum-based fi nite element model while naturally introducing length-scale to cure mesh pathology. In addition, internal variables, such as plastic dilatancy and plastic fl ow direction, are now obtained directly from granular physics, without introducing unnecessary empirical relations and phenomenology. Microstructural information, such as force chain length, coordination numbers, and pore size distribution are compared with permeability inferred from lattice Boltzmann fl ow simulations to explain the mechanism that leads to the formation of fl ow conduit during strain localization.