Step-path failure of rock slopes with intermittent joints

Step-path failure is a typical instable mode of rock slopes with intermittent joints. To gain deeper insight into the step-path failure mechanism, six rock slopes with different intermittent joints are studied using the 2D Particle Flow Code (PFC). Three different step-path failure modes, i.e., shear, tensile, and mixed tensile–shear failure, are observed by focusing on the crack initiation, propagation, and coalescence in the rock bridges. The cracks develop progressively in the rock bridges, which induce the intermittent joints to coalesce one by one from bottom to top under the action of gravity. The tensile cracks that often appear in the main body and at the crown are nearly vertical to the step-path failure surface. The step-path failure in a rock slope with intermittent joints can be divided into four stages in terms of both stress and crack development in the rock bridges, i.e., elastic deformation, failure of rock bridges at a lower position, progressive failure of rock bridges upward, and final block slide. Therefore, reinforcement is suggested to be applied to the lower part of the slopes. Three equations for calculating the factors of safety are derived with respect to the three failure modes, in which the degree of joint coalescence is considered.