Off-Center Tetrahedral Wedges

Tetrahedral wedges in rock slopes can have symmetric and asymmetric shapes. Asymmetry is commonly recognized as differences in dip angles of the sliding planes. This form of asymmetry is known to influence the kinematic feasibility and stability of a wedge. Asymmetry also influences the appearance of wedges and therefore the ability to recognize wedges in rock faces and in data from rock masses. The relative orientation of the sliding planes in relation to the lower and upper slope faces is also part of the asymmetry system. In particular, the direction of the line of intersection which determines the sliding direction of two planes, relative to the direction of the slope of the rock face introduces an additional type of asymmetry. This form of asymmetry is defined here as off-center wedges. A detailed terminology for asymmetric tetrahedral wedges is presented and the implications for kinematic feasibility, sliding mechanism and stability analysis are discussed. A field example from Auckland New Zealand is presented.