How does the angle of repose affect the stability of a spoil pile?

The angle of repose directly determines the maximum steepness at which a spoil pile can remain stable. The angle of repose is the steepest angle at which a pile of granular material, such as soil, gravel, or sand, will naturally form without collapsing. It's the angle between the horizontal plane and the slope of the pile. Each type of material has a different angle of repose, depending on factors such as particle size, shape, moisture content, and cohesiveness. Materials with larger, more angular particles and higher cohesiveness tend to have higher angles of repose, ....