Abstract <p>The article describes the research findings on slope stability in open pits and quarries Transbaikalia, at the stages of exploration, mine planning, design and redesign. The feature of the test surface mines is tectonic disturbance of rock masses, including zones of faulting, crushing and compression. Earlier, such geomechanical assessment was carried out using traditional approaches, and the conclusions lacked estimates of probability of slope failure in open pits. Modern regulations on pitwall stability recommend quantitative estimation of slope failure probability using the probabilistic analysis and statistical testing, for example, the Monte-Carlo method. Owing to the statistical testing and its results, it is possible to quantitatively assess probable risks of slope failures in open pits and, also, to offer better defined requirements on the input data accuracy.</p>