Geomechanical Characterization of a Weak Sedimentary Rock Mass in a Large Embankment Dam Design

Abstract

The geomechanical characterization of a weak and tectonically undisturbed sedimentary rock mass (“molasse”), carried out for the design of a large embankment dam in the Kurdistan Region (Iraq), is presented. In view of the relevant dimensions of the dam and of its main ancillary works, the rock mass characterization has represented one of the basic focus of the geological and geotechnical investigations. However, various uncertainties have been considered to potentially affect the final estimate of the engineering properties of rock masses in the context of the present study. In particular, besides the natural variability of weak rocks characteristics and the well-known difficulties in their realistic estimation, uncertainties may also arise from the potential incompleteness of the basic data available, mainly due to time and budget limitations. In order to quantify such uncertainties and adequately incorporate their effects into the design process, a probabilistic approach based on Monte Carlo method has been adopted to determine the probability distribution functions describing the rock mass strength parameters. A practical example of application of the followed probabilistic approach to the design of large excavation rock slopes is briefly illustrated.