Analysis of two variants of sequential excavation of a cross section of the Bôrik Tunnel

The Bôrik tunnel has been designed as a double tube tunnel intended for one way traffic. Both tunnel tubes with the lengths of 999 and 993 meters are mutually interconnected by two escape entries. The Bôrik tunnel is part of the D1 Mengusovce Jánovce motorway structure. The tunnel goes through sound und semi rock forquarternary basic (dolomite) und quarternary sediments (in the tunnel portals glacial und deluvial sediments).The tunneling project operations were carried out by Geoexperts Firm (fig. 1 - variant No 1). The alternative tunneling project operations were carried out by Profesor Ing. J. Hatala, CSc. (fig. 2 variant No 2). During excavation of the tunnel a rock pillar of varying thickness is considered. The arbitration oh both variants was realised using mathematical modelling. The mathematic model involves: The effect of rock bolts on the stability of the rock massif, The influence of shotcrete on the stabilization of the tunnel tubes, The effect of the protective umbrella in the portal section, relaxation of stresses in the rock massif after partial excavation, Time sequence execution of each excavation.The Mohr Coulomb constituded model was used in the analysis. On the basis of the analysis using mathematical modelling, it is possible to state that the texcavation of the Bôrik tunnel is better in terms of stress state with variant number one