This paper presents the results of engineering characteristics of the rock masses and tunnel support design studies, carried out at the Daroongar dam site, northeast of Iran. The diversion tunnel will be driven in rock mass, consisting of sandy limestone and limy marl of Upper Cretaceous age. Studies were carried out both in field and laboratory. Field studies include discontinuity surveying, core drilling and sampling for laboratory testing. Laboratory studies were performed on core specimens taken from the boreholes, in order to determine physical and mechanical properties of the main lithotypes. Empirical and numerical methods were used for tunnel design. The tunnel grounds were divided into sections with respect to the rock mass geological engineering properties. Rock masses were characterized using Rock mass rating (RMR), Rock mass quality (Q) and Geological strength index (GSI) system and the tunnel ground support types and categories were determined according to the RMR and Q-system. The strength and modulus of elasticity of rock masses are determined using the Hoek–Brown empirical strength criterion. The interaction of the recommended support systems by empirical methods with the rock masses were analyzed by two dimensional universal distinct element code (UDEC). It was seen that empirical and numerical approaches showed similar results. This indicates that more reliable support design could be achieved by using the distinct element method together with the empirical methods.

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