Modeling the instability of rock slopes consisting of alternating weak and hard layers

In this study, the role of weathering behavior of three types of rocks (A, B, and C types) in the instability of three trenches constructed along the Khorramabad-Pol-e-Zal highway (West of Iran) has been evaluated. The trenches containing the A and B rock samples have experienced considerable instability due to the low durability of these samples and the alternation of stiff and weak layers. Heavy rains exacerbate this instability. Water infiltration through tectonic discontinuities and weathered structures has led to saturation-induced expansion of the weak layers. Based on the kinematic analysis, toppling, wedge sliding, and rock fall were identified as the most important failure mechanisms in the trenches. The results of numerical modeling by UDEC indicated that the slopes were unstable under a natural state, where a large deformation was observed due to falling unstable blocks of the slopes. Analysis results by Rocfall software also showed that the height and kinetic energy of rock blocks are higher in hard rock parts of the slopes. Overall, there is reasonable compliance between instabilities observed in natural form and those obtained by the numerical simulations.