Tunnel excavation leads to a redistribution of stress in rock mass. Deformations of the mass, caused by the progression of excavation, alter the primary state of stress in the mass and cause stress in the primary supports. Available computer methods in geoengineering, linear and non-linear constitutional equations, as well as 2D and 3D models accompanied by the use of developed computer programs, tends to be much more developed and sophisticated than existing knowledge and descriptions of geotechnical properties of materials used in the model. The calculation results are particularly dependent on the chosen model and values sourced from the relevant geotechnical parameters. Intensive measuring during tunnel works, undertaken in carbonate rock mass in karst found in Croatia has shown that the measured deformations are significantly greater than that gained from calculations that use stiffness parameters obtained from existing correlations to rock mass classifications. Furthermore, the measured forms of deformation based on depth significantly vary from those calculated, i.e. anticipated by the project. Such measurements have allowed for the development of a new approach in determining the deformation modulus of carbonate rock mass in karst found in Croatia.
The paper presents 2D and 3D numerical simulations for excavation of the Bobova Tunnel on the D404 national roadway and its comparison with measurement results. Bobova Tunnel, excavated in 2005 is located on the D404 national road and passes under the Vežica – Šušak town section in Rijeka. The tunnel is 189.50 m long and has been constructed as a full three-lane tunnel. Both simulations utilise a new approach in determining rock mass stiffness in karst found in Croatia, which in turn provides more reliable prediction of deformations in geotechnical structures.

tunnel construction, numerical modelling, karst, rock mass stiffness, monitoring