Stability of Rock Protection on Slopes

The stability of rock protection on slopes attacked by a flow requires two conditions. The first is the resistance to sliding that is provided if the ratio of tangential forces to normal forces on one or several rock layers is less than the tangent of the angle of friction of the layers on their support. The second is the resistance to wrenching of the surface layer blocks and is covered by equations derived from the Shields criteria. This paper proposes a new approach to two factors in the analysis, namely: (1) For downslope flow the hydrostatic pressure gradient is not vertical but normal to the slope, and thus existing equations expressing the effect of slope on the threshold shear stress are modified; and (2) a condition of stability that involves the bearing angle of a surface‐layer block thrusting on neighboring stable blocks that is wider than the commonly used angle of repose.