Distinguishing between single and double plane sliding of tetrahedral wedges using the circle method

• The circle method of wedge analysis provides an improved stereographic technique.
• Method able to distinguish between single plane and double plane wedge sliding
• Method used to define the types of wedges that can be formed with other poles by using the circle method

A tetrahedral wedge of rock can slide on one or both of the bounding discontinuity surfaces. The test to identify these two mechanisms can be performed on a stereograph based on the orientation of the two discontinuities, their line of intersection and the slope face. An alternative stereographic method involves identifying the great circle, known as a π-circle, linking the discontinuity poles and comparing this plane with the slope face orientation. A kinematically feasible wedge is double plane sliding unless the following two criteria are met. 1) One of the poles is within the daylight envelope for the slope face and 2) that pole lies between the dip direction of the π-circle and the direction opposite to the slope direction of the excavation face. These criteria are readily observable on a stereograph. The boundaries for poles capable of forming single and double plane sliding wedges in combination with another pole can be marked as zones on the stereograph.