Angle of Repose - Zone of Influence

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The Angle of Repose

The angle of repose or the angle of rest is the angle that a material will naturally support itself at. Think of a pile of sand, when it is delivered out of the truck it sits up in quite a nice heap this is the angle of repose.

Over time the influence of the weather and people will cause the heap to spread and lower however generally speaking the weather will not affect the material when it is in the ground. 

The angle depends on the shape and size of the individual grains and how they move over each other.

Material	Angle Of Repose
Wet Sand	45o
Granite	35o - 40o
Dry sand	34o
Crushed Asphalt	30o - 45o
Loose Dry Gravel	30o - 45o
Dry Lump Clay	25o - 40o
Natural Gravel with Sand	25o - 30o
Water filled sand	15o - 30o
Wet Excavated Clay	15o

Zone of Influence

Therefore anything inside the Angle of Repose will support itself and not want to collapse into a  excavation. 

However any thing that is outside the Angle of Repose is in the Zone of Influence. Anything in this zone has the potential to collapse into a excavation if it is affected by weather, water, people or machines or anything else that could cause it to move.