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Comparison of predicted and actual conditions of the rock mass in the tunnel Crna Brda

Tunnel Crna Brda is located near city of Omiš at Zagreb-Split-Dubrovnik highway in Croatia. The interactive design method was applied in the tunnel design. Interactive design method integrates the empirical, rational and observational approaches in the geotechnical design of the tunnel. Also allows a continuous design or design in two phases. First phase of the design takes place prior to the tunnel construction. Solutions for the underground excavation support were done based on site investigation activities and other bases using the empirical and rational approaches. Second phase of the design takes place during the tunnel construction. Engineering-geological tunnel mapping was done during the excavation in order to define the support system. Verification of the tunnel support system during the construction phase was done using the actual data obtained from the engineering- geological mapping and the monitoring. Thus, the actual rock mass quality along the tunnel was determined and the tunnel underground excavation support measures were optimized. Due to the complex conditions present in the rock mass, the discrepancy between estimated and actual rock mass conditions can hardly be avoided, and likewise, a certain amount of discrepancy between the predicted and actual support systems is also to be expected. Discrepancy, although acceptable, should be within some limits of ±20% in order to control construction cost and construction time. The aim of this paper is to examine and compare the results of engineering geological exploration works in the design phase and during the construction of tunnel Crna Brda.

Engineering geology; Rock mass classification system; Tunnel support system; Interactive design

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