arXiv subjects

Bimal Chhushyabaga

Publications and source records attributed to Bimal Chhushyabaga.

2 recordsLinked to original sources

arXiv2026

Investigating frictional instability due to pressurization in granular media: insights from coupled computational fluid dynamics discrete element method

Fluid pressurization can reactivate subcritically stressed granular layers in faults, slopes, and injection-perturbed reservoirs, but grain-scale feedbacks among pressure diffusion, drainage, and contact-network degradation remain unresolved. Here, 3D coupled CFD-DEM simulations investigate pore-pressure-induced reactivation of confined, fluid-saturated granular shear layers under imposed shear stress. Strain-controlled tests define the Mohr-Coulomb strength envelope; stress-controlled simulations then impose subcritical shear stresses while basal pore pressure increases under drained and undrained conditions. Instability is governed not by pore pressure alone, but by its coupled evolution with effective stress, drainage, dilation or compaction, hydraulic connectivity, and granular fabric. Undrained boundaries retain excess pore pressure, whereas drained boundaries maintain vertical gradients and suppress excess pressure. Internal fields reveal alternating dilation and compaction bands and reorganization of a porosity-derived permeability proxy, showing that hydraulic pathways evolve during deformation. Micromechanical diagnostics identify localized particle rotation, force-chain reorganization, porosity redistribution, and coordination-number variations controlled mainly by imposed shear-stress level rather than drainage. Second-order fabric metrics show that post-failure weakening coincides with loss of directional force-chain organization, especially at lower shear. Friction-velocity and friction-porosity trajectories indicate a transition from dilatancy-dominated strengthening to pore-pressure-driven weakening. Viscous-number scaling partially organizes the low-Iv creeping response, 10^-8 <= Iv <= 10^-5, but not onto a unique local rheology. These results clarify how drainage-controlled hydromechanical feedbacks and fabric degradation convert pore-pressure forcing into instability.

cond-mat.soft↗

arXiv2025

On the interaction of dilatancy and friction in the behavior of fluid-saturated sheared granular materials: a coupled Computational Fluid Dynamics--Discrete Element Method study

Frictional instabilities in fluid saturated granular materials underlie natural hazards, including submarine landslides and earthquake initiation. Experiments show distinct failure behaviors under subaerial and subaqueous conditions due to coupled deformation, interparticle friction, and particle fluid interactions. We use three-dimensional coupled computational fluid dynamics, discrete element method (CFD - DEM) to investigate collapse and runout of dense and loose granular assemblies in both environments. Parametric analyses show that pore pressure evolution controls failure mode in saturated settings (fast vs slow sliding), consistent with prior laboratory experiments and lattice Boltzmann discrete element simulations: dense assemblies stabilize via dilation, whereas loose assemblies compact rapidly and transiently fluidize. At mesoscale, we coarse grain particle contact statistics and Eulerian fluid fields to define apparent friction and normalized pore pressure, and organize inertial and viscous responses using log10(In/Iv). Spatiotemporal analyses of these coarse grained fields reveal strain rate dependent behavior governed by evolving porosity and effective stress. In both environments, friction in failure shear zone is rate-strengthening with respect to inertial number (In, for dry) and viscous number (Iv, for fluid-saturated). We further utilize mesoscale stress framework to compare evolution of pore pressure in CFD - DEM of subaqueous slope collapse with an analytical solution for development of failure front, using inputs derived from numerical triaxial DEM tests on same assemblies. The analytical model reproduces steady-state excess pore pressures and captures fluid-particle coupling, but mismatch near failure onset suggests transient frictional effects. These results support physics-based hazard models and improve mechanistic understanding of saturated granular failure.

cond-mat.soft↗