## 3 Applying the Methodology to the Example of Dabar Power Tunnel  
### Geological Setting and Problem Statement  
The Dabar hydrotechnical tunnel, which has a total length of 12 km, is located in the south-eastern zone of the Republic of Srpska, in Bosnia and Herzegovina. It is used as a derivation pressure tunnel as part of a hydropower station of the same name, which is one of the power plants in the Trebisnjica River hydroelectric system. The terrain in the wider zone of the tunnel is a high mountain area with average altitudes between 800 and 1100 m above sea level, featuring prominent mountain massiffs, among which are located separated karst fields. The mountains and karst fields have an elongated shape in the direction of the Dinaric extension, northwest to southeast. The karst fields, which gradually descend towards the Adriatic Sea, are divided into four horizons. The degree of karstification of the limestone rock mass differs significantly on the horizons depending on the lithological composition, structure, age, and tectonic and non-tectonic movement at the localities. The locations of Dabar accumulation and Dabar tunnel and the geological map of the area with key information are presented in Figure 2.  
Geological investigations of the terrain in the tunnel area were conducted in several phases, starting in 1962. The emphasis was first placed on the regional tectonic complex and hydrogeology of the wider research area. In the later phase preceding the main design, six exploratory boreholes were drilled with a total length of 692 m. [PERSON]'s tests were conducted within the boreholes, and piezometers were installed for long-term monitoring of underground water levels between 1985 and 2001. Samples were taken for laboratory testing and sedimentological, petrological, and micropaleontological analyses. In the next phase, the main design was completed and  
phase of project development, a total of 10 exploratory boreholes (950 m in total) were sunk, seven of which were equipped with piezometers. In addition, in three boreholes, pressuremeter tests were conducted in order to determine the deformable properties of the rock mass. Remote sensing techniques were applied to determine the geological structure in the area of the tunnel on a 1:5000 scale map to locate faults, folds, and instability phenomena, whereas satellite images were used for the analysis of regional faults at a larger scale. A total of 20 samples were taken from an additional single 320 m deep borehole for strength and deformability tests (compressive and tensile strength, moisture content and density, velocity of wave propagation V\({}_{\mathrm{p}}\) and V\({}_{\mathrm{s}}\), and modulus of elasticity of intact samples). Additionally, one research gallery was excavated in which tests were conducted in situ using a hydraulic jack to determine the stiffness parameters of the rock mass in field conditions. The geophysical investigation was conducted to interpolate the measurement results between the boreholes. This contributed to the formation of the geological model along the axis of the tunnel. Based on the results of all investigations, a geotechnical model of the terrain with 18 geotechnical units was formed; the section in limestone is shown in Figure 3. As seen in the figure, the four geological units, with a total length of some 8.1 km in the layout of the Dabar tunnel, mostly pass through Cretaceous limestone (K\({}_{2}\)\({}^{3}\)). The remaining 4 km of the tunnel (not shown in Figure 3 due to clarity) passes through molasse sediments, represented by conglomerates, sandstones, marls, and clays of the Eocene-Oligocene age (E\({}_{3}\),O\({}_{1}\)). Within the limestone section, the tunnel also passes through Eocene limestone sediments (Pc,E) for a total length of approximately 350 m. This geological unit has different geotechnical properties from the Cretaceous limestone and was not considered in this study.