Kinematic analyses of sliding and toppling failure of double free face rock mass slopes

Free face geometry shape plays an important role in determining failure and evaluating slope stability. Kinematic analysis is a very effective method in solving these issues stated above. Most kinematic analyses for rock mass slope stability mainly focus on the research of failure mode and maximum safe slope angle for single free face slopes. However, there are many slopes with double free face along strike of cut slope in engineering applications. In this paper, research on rock slope stability is extended to slopes with double free face. The corresponding sliding modes are divided into four types: (a) plane sliding along a discontinuity; (b) wedge sliding along a single discontinuity plane; (c) wedge sliding along the intersection line of two discontinuities and (d) toppling failure. On the stereographic projection, sliding zone for plane and wedge sliding can be marked as the area formed by the true dip direction lines of the two faces that form the double free face and the friction circle where the dip vector or the line of intersection vector should lie. The toppling zone can be marked as the area formed by the true dip direction lines of the two faces that form the double free face, friction circle and the periphery of the stereographic plot where the normal vector to the discontinuity should lie. The procedure to obtain the maximum safe slope angle for a double free face rock mass slope and the design principle to estimate the cut slope angle are suggested. Based on the method presented above, Shengjipo double free face rock mass slope, which is located in Zigui county, Hubei Province, is used as a case study to illustrate determination of failure modes and maximum safe slope angles.