Figure 15.20
Slope stability. (A) The angle of repose is the steepest slope a material can maintain while remaining stable. It is a result of the relationship between gravitation and friction among particles, and it varies depending on the shape, size, and wetness of those particles. (B) If the resistance force (Fr) is equal to or greater than the downslope force (Fd), the material will not move. If the resistance force is less than the downslope force, the material will move. In this example, the downslope force is increased by steepening of the slope, as might occur where a hillside is cut by a new road.