Stability analysis of large rock slopes for Sardasht dam hydraulic power plant trenches considering rock cleavage

The site for Sardasht dam and its hydraulic power plant contains metamorphic slate rock masses with distinguished cleavage surface characteristics leading to reduced rock mass strength. Hence, stability analysis of the surrounding structures, underground spaces and slopes, is of great importance. Stability analysis of the slope, adjacent to the dam, was carried out for the three conditions of without cleavage, considering cleavage and inclusion of fractures zones, based on limit equilibrium and finite difference methods using SLIDE and FLACSLOPE 2D codes, respectively. The results indicate that the slope slide was not found safe in the presence of cleavage and fractured zones. For assurance, further statistical analysis was also carried out on the slope stability. The accumulative distribution function indicated that the confidence coefficient for 68% of the data was found to be less than 1.7, which confirms the extreme influence of cleavage on the slate rock mass strength. Therefore, the 1:6 slope presented in the drilling map preliminary report is unstable.