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  Influence of Material Models for the Effective Design of the Primary Lining

  Using of the finite element method issued a significant impact of static assessment of tunnel primary lining. Design can be effective and more realistic. For this calculation can be employed various behavioral models. The first question for geotechnical engineers, before modelling is find the proper numerical description of problem and then answer to link with a real situation.As a result of model research, only two material models are considered and can submit a favorable response.The Mohr – Coulomb model is a widely used model because results are on the safe side. This model failure criterion represents the linear envelope that is obtained from a plot of the shear strength of a material versus the applied normal stress. In geotechnical engineering it is used to define shear strength of soils and rocks at different effective stresses. However, this model is not optimal economically.Second material model which can be helpful for design optimization is HoekBrown model. The Hoek–Brown failure criterion is an empirical stress surface that is used in rock mechanics to predict the failure of rock.The original version of the Hoek–Brown criterion was developed for the design of underground excavations. An update of the criterion was presented in 2002 that included improvements in the correlation between the model parameters and the geological strength index (GSI).The basic idea of the Hoek–Brown criterion was to start with the properties intact rock and to add factors to reduce those properties because of the existence of joints in the rock. Although a similar criterion for concrete had been developed in 1936, the significant tool that the Hoek–Brown criterion gave design engineers was a quantification of the relation between the stress state and Bieniawski’s rock mass rating (RMR).Designer can use other behavioral models which are more suitable for various rock environment resulting in more economical design. The main problem is relatively wide range of developed models. Every model can lead in unpredictable result and pricking the right model can be hard.Those questions can be interesting especially by design of long tunnels in hard environment conditions. Tunnel Soroška is designed as 4.2 km long road tunnel in karst rock. Employer decided to divide construction into two phases. In the first phase will be built only one tunnel tube for both directions.

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