## 5 Discussion  
A new approach for the numerical modelling of tunnel constructions at a level sufficient for practical application was proposed. In this regard, the research dealing with the method of cooperation rings has been almost finished.  
However, the problems in numerical modelling of the tunnel construction are comprehensive and require further attention in the following areas:  
* the possibilities of staging the progress of driving a tunnel using the \"construction stages\" and agreement with the modelled master. The driving stages are highly approximated (as in practice), and depend on time factors, with the primary lining being applied after driving, and another section then being excavated at the length of burden. During this relatively short time, radial deformations occur only partially (deformation load) and can only be stabilised several driving cycles later. These radial deformations depend on not only the driving progress but also the fundamental rheological behaviour of the rock mass as a response to this action. Numerical models partially disregard this information. An equilibrium state is found between the individual construction stages of a spatial numerical model that does not occur in reality. The numerical model de facto simulates the following procedure: driving, partial mobilisation of radial deformations or omission, lining implementation, stabilisation of radial deformations of the rock mass, balancing, etc.
* In contrast to the theory for reinforced concrete, calculation based on the theory for cooperation rings does not deal with tensile stresses in the cross-section caused by a large eccentricity in the load. While a tensile stress is excluded from operation in the theory of reinforced concrete, this is  
Figure 14: Stresses in individual elements of the lining (steel and concrete) after recalculation according to the redistribution coefficients.  
not the case in the theory for cooperation rings. When interpreting the results, it is possible to accept an alternative for tensile crack occurrence in concrete and the stress redistribution to steel elements, which have a high reserve of load-bearing capacity in this case. The stated conclusion is acceptable according to the principles of the NATM, where the primary lining forms a significant, but temporary structure.
* The method of cooperation rings, based on which the Homogenisation software application was implemented, is designate for circular cross-section tunnel profiles. However, a comparison between Alternatives I and II revealed a difference of \(<1\%\) in the internal forces, indicating that this software/method can be used even for generally non-circular profiles. In other studies involving a critical analysis of the stresses in individual elements of the lining, i.e., steel and concrete, the difference in the application of the Homogenisation software was more significant [39]. In particular, the most problematic point was where the counter-arch connected to the sides of the lining, i.e., the point where the curve radii changed. The stress in the steel differed by 23% in comparison with the 3D model, whereas the differences for the stress in the concrete were small, not exceeding 1%.