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Justification of seismic triggering of large prehistoric rockslides that originated on the slopes of anticlinal ridges armoured by thick carbonate units has been performed by examples of the gigantic Seimareh rockslide in Zagros (Iran) and two structurally similar, though much smaller rockslides in Dagestan (Greater Caucasus, Russia). Such structural and geomorphic conditions allow precise reconstruction of the pre-slide topography of the studied sites that increases reliability of their back analysis significantly. Linear dimensions of landslides are much larger than thickness of the siding block that makes the simplified 2D numerical modelling of these slopes quite realistic. The pseudostatic analysis performed at the first step confirmed that the study slopes could not fail without strong earthquakes. However, further dynamic analysis performed by use of the Newmark method allowed estimating characteristics of strong motions that could result in formation of rockslides that had converted in long runout rock avalanches. Possible uncertainties and open problems are discussed as well.

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The deterioration of rock strength due to cyclic fluctuations in the groundwater level in drawdown regions influences bank slope stability. Based on wetting–drying cycling and uniaxial compression tests of sandstone specimens, the intact rock strength deterioration characteristics were analyzed. Considering different types of rock mass discontinuities, the rock mass strength deterioration features were shown. The results of rock mass strength deterioration characteristics were then applied in sandstone slope stability analysis. Using the finite element method, the safety factors of the slope under different wetting–drying cycles were computed based on the generalized Hoek–Brown failure criterion. Meanwhile, statistical distribution features of strength parameters were considered, and safety factor distribution of studied slopes was obtained with Monte Carlo simulation. The results show that rock mass deformation modulus decreased during wetting–drying cycling. The mean safety factors of the slope with any type of discontinuities were reduced by wetting–drying cycling in probabilistic analyses. Wetting–drying cycling plays an important role in damaging slope stability at initial stages since the degree of rock mass strength deterioration is remarkable during initial wetting–drying cycles. However, the rock mass strength and safety factor of the slope are reduced gently after 10 wetting–drying cycles. This research presents the phases of the effect of wetting–drying cycles on sandstone slope stability in drawdown regions.

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