Characterization of wet granular avalanches in controlled relative humidity conditions

• The relation between characteristic angles, relative humidity and cohesive state has been obtained.
• Remarkable difference between first and other avalanches has been found.
• The concept of “hygroscopic equilibrium time” is defined.

This work focuses on the influence of the relative humidity (essentially due to atmospheric conditions) on the many granular media behaviours. To this end, the experimental evolution of the avalanche characteristic angles of continually tilted granular packing was studied for a wide range of relative humidities in very well controlled conditions (between 5 and 90%). The stability angles were measured for fully developed avalanches. The relationship between the relative humidity (ϕ) and cohesion of granular media (directly related to cohesion forces between grains) was then established to identify the different cohesive states of a wet granular medium using a reliable and reproducible testing methodology. Finally, a relationship between the hygroscopic equilibrium time and the stability of the granular packing is discussed.

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