A constitutive law for dense granular flows was proposed by Pierre Jop, Yoël Forterre, and Olivier Pouliquen. The study addresses the challenge of modeling dense granular flows, which can behave like solids, liquids, or gases depending on conditions. The authors developed a visco-plastic constitutive law that captures the behavior of granular materials in dense regimes, where they flow like a liquid. This law is based on the inertial number, a dimensionless parameter that relates shear and normal stresses. The law accounts for the yield criterion, where flow is not possible below a critical shear stress, and the complex dependence of shear rate on flow. The model was tested through experiments of granular flows on a pile between rough sidewalls, where a complex 3D flow pattern develops. The model, without any fit parameters, successfully predicted the flow shape and velocity profiles. The rheology was generalized to three dimensions, with the granular material described as an incompressible fluid with an internal stress tensor dependent on shear rate and pressure. The effective viscosity diverges to infinity at zero shear rate, ensuring the existence of a yield criterion. The model was validated against experimental data, showing good agreement in predicting the free-surface inclination, velocity profiles, and thickness of the flowing layer. The results indicate that the proposed constitutive law can quantitatively describe complex 3D granular flows without fit parameters. The study also highlights the importance of sidewalls in dense granular flows and shows that the thickness of the flowing layer depends on the channel width and flow rate, not on intrinsic properties of the granular material. The model represents a minimal yet effective approach for understanding granular flows, with potential applications in geophysical and industrial contexts. However, the model's yield criterion is simplified and does not account for more complex behaviors such as shear bands and hysteretic phenomena.A constitutive law for dense granular flows was proposed by Pierre Jop, Yoël Forterre, and Olivier Pouliquen. The study addresses the challenge of modeling dense granular flows, which can behave like solids, liquids, or gases depending on conditions. The authors developed a visco-plastic constitutive law that captures the behavior of granular materials in dense regimes, where they flow like a liquid. This law is based on the inertial number, a dimensionless parameter that relates shear and normal stresses. The law accounts for the yield criterion, where flow is not possible below a critical shear stress, and the complex dependence of shear rate on flow. The model was tested through experiments of granular flows on a pile between rough sidewalls, where a complex 3D flow pattern develops. The model, without any fit parameters, successfully predicted the flow shape and velocity profiles. The rheology was generalized to three dimensions, with the granular material described as an incompressible fluid with an internal stress tensor dependent on shear rate and pressure. The effective viscosity diverges to infinity at zero shear rate, ensuring the existence of a yield criterion. The model was validated against experimental data, showing good agreement in predicting the free-surface inclination, velocity profiles, and thickness of the flowing layer. The results indicate that the proposed constitutive law can quantitatively describe complex 3D granular flows without fit parameters. The study also highlights the importance of sidewalls in dense granular flows and shows that the thickness of the flowing layer depends on the channel width and flow rate, not on intrinsic properties of the granular material. The model represents a minimal yet effective approach for understanding granular flows, with potential applications in geophysical and industrial contexts. However, the model's yield criterion is simplified and does not account for more complex behaviors such as shear bands and hysteretic phenomena.