Angle of Repose

An angle of repose is the maximum angle from the horizontal that a pile of granular material can have and still be stable. Stable means that the material does not keep sliding down unless something changes. This can apply to a granular material, such as sand, poured on a level surface. The sand will form a cone. The angle of repose is the angle of the side of the cone of sand from the base.

The angle of repose for any particular material is related to the density, surface area and shapes of the particles, and the coefficient of friction of the material. A material with a larger angel of repose will form a steeper pile.

Angle of repose is used to:

• design machinery used to hold and transport granular material such as conveyor belts;
• calculate the danger of avalanche;
• determine if a slope is likely to collapse;