Rock slope stability analysis has been a challenging problem for civil and mining engineers. There are several modes of failure in which a rock slope can fail; a plane failure is one of them. In recent past, a generalized expression has been presented for the factor of safety of the rock slope against plane failure. The expression considers several parameters that govern the stability of the slope. These parameters are: inclination of the slope face, inclination of the joint or discontinuity plane, unit weight of the sliding rock mass, shear strength parameters of joint materials, depth of tension crack, depth of water in tension crack, surcharge and seismic loadings, and the stabilizing force and its inclination. Though the analytical expression can be used to calculate the factor of safety, practising engineers generally prefer the use of design charts. A numerical example is illustrated to explain the calculation steps so that the developed design charts can be used conveniently.
Civil and mining engineers generally face a challenge of getting realistic values of the factor of safety of the excavated or natural rock slope against plane failure. This happens mainly because of heterogeneous and anisotropic characteristics of rock masses. The rock slopes often have discontinuities in various forms, resulting in different types of slope failures, such as plane failure, wedge failure, circular failure, toppling failure and buckling failure (, , , , ). A plane failure (aka block sliding) generally occurs in hard or soft rock slopes with well defined discontinuities and jointing, e.g, layered sedimentary rocks, volcanic flow rocks, block jointed granite, foliated metamorphic rocks ]3[. There are several parameters that govern the stability of the rock slope against plane failure, such as inclination of the slope face, inclination of the joint or discontinuity plane, depth of tension crack, depth of water in tension crack, shear strength parameters of the joint material at the failure plane, unit weight of rock, stabilizing force and its inclination, surcharge, and seismic loads (, , , , ). In view of the fact that surcharge loading caused by structures, machines, etc, is a common destabilizing force in most mining and civil engineering applications, Chukka et al.  developed an analytical expression considering both surcharge and seismic loadings.
Hook and Bray  presented most of the basic methods of limit equilibrium analysis for rock slope stability against plane failure condition. Ling and Chang  presented an analytical expression for the factor of safety of the rock slope against plane failure induced by seismic force, ignoring the possibility of upward direction of vertical inertial seismic force, and without considering the surcharge and the anchoring force. Hook  described the idealisation of the rock slope failures in Hong King as plain failures and presented an analytical expression for estimating the factor of safety, considering many practical aspects including seismic loadings, but this expression does not incorporate surcharge and seismic force with all its possible directions.