We study gravity-driven granular flows over a wide incline with a slip base using 3D Discrete Element Method (DEM). Unlike a no-slip base that typically produces a shear-dominated Bagnold velocity profile, flows in wide inclines with slip boundary create a complex flow profile for angles below the friction angle. This consists of a fluid-like shear zone that localizes near the boundary and coexists with a solid-like plug zone. We quantify the interface between these flow regimes by a shear zone height, \(\delta \) . We examine different flow properties for several pile heights, H, mean grain diameters, d, and slope angles, \(\theta \) . We show that by using a critical value for the microscopic non-dimensional granular temperature, \(\Delta _c\) , the shear zone height, \(\delta \) , can be estimated. We observe that \(\delta \approx 6d\) across all granular systems we studied. Interestingly, the 6d shear zone height obtained by our simulations is in agreement with the findings of the minimum effective orifice length, i.e. \(D\gtrapprox 6d\) , in funnel flows presented by the Beverloo law. This suggests that the same length scale and flow properties may drive the two seemingly different flow conditions. We show that the shear zone behavior is best described by a linear \(\mu (I), \phi (I)\) -rheology while the transition region between the shear zone and the plug zone follows non-local \(\mu (I,\Delta )\) rheology. The rheological models can verify our DEM results, particularly by predicting the terminal velocity, which is the solid-like flow velocity. Overall, we provide insights about the dual flow regime in a wide incline with a slip base and identify rheological models that capture the flow properties and regime transition.
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