I have encountered a very strange idea from my Professors and I would like to get your help if possible. Let me summarize you first my and their believes;

My Believe

A granular material at low to medium density and irrespective of degree of saturation can undergo through the range of frictional to collisional mechanism kinematically depending on rate of shear. At low speed, it is frictional while at high speed, collisional. The mechanism also transforms from frictional to collisional when the flow rate changes from low to high.

The others’ Opinion

A dry granular material behaves always frictional irrespective of rate of shear. They mentioned, “What process changes or transforms a frictional dry debris flow to a collisional mechanism when the shear rate increases?” They explicitly said that it can not be transformed “kinematically”. They further mentioned that a collisional mechanism, perhaps, can exist but only in case of saturated rapid debris flow and that is not due to “kinematics” but it is due to the pore water turbulent (due to the momentum transfer of water to granules) and the whole material acts as a fluid.

It has a kind of implication that no need to consider the kinetic-collisional mechanism and the frictional model alone can explain the behavior of debris flow in wide range.

Do you have experimental evidences that may show a debris or granular flow changing from frictional to collisional mechanism due to shear rate increase? Can you explain me this confusion with evidences if possible so that I can discuss with them.

Please I am waiting your response and your help is very significant.

Thanks,

Abraham,
PhD student
University of Alberta
Edmonton, Canada

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