If the particles in the suspension are not neutrally buoyant, then the additional effect of settling also takes place. Pudasaini (2011) used the above constitutive relations to establish a scaling law for the sedimentation time. It is found analytically that the macro-viscous fluid settles much faster than the grain-inertia fluid, as manifested by dispersive pressure.
Given the same time, the macroviscous fluid is settled 6/5 unit length compared to the unit length settlement of the grain-inertia fluid as measured from the nose-tip of the flowfront that has already settled to the back side of the debris. Therefore, the macroviscous fluid settles (completely stops to flow) 20% faster than the grain-inertia fluid. Due to the dispersive pressure in grain-inertia fluid, the settlement process is delayed by 20% for the grain-inertia fluid than for the macroviscous fluid. This is meaningful because particles are more agitated due to higher dispersive pressure in grain-inertia fluids than in macroviscous fluids. Once the material comes close to rest, these dispersive forces (induced by the quadratic shear rate), are still active for grain-inertia fluid but macroviscous fluid settles relatively faster because it is less dispersive. This provides a tool to approximate and estimate the final settlement time (the time at which the entire fluid body is at rest). These are mechanically important relationships concerning the settlement time and the settlement lengths between the grain-inertia and the macroviscous fluids.