Defining the optimal distance between technological sequences during tunnel excavation in poor rock mass

Abstract: When excavating tunnels in urban areas with shallow overburden in poor rock mass, the deformations are very pronounced, which can result in serious potential risks to the safety, costs and time of tunnel construction. In the Kobilja Glava tunnel, which will be part of the project connecting Vogošća with Sarajevo and connecting the city center of Sarajevo with the A1 motorway on Corridor Vc, monitoring of displacements was conducted in a specific section of the left tunnel tube over a length of 80 m, in terms of various distances between the top heading excavation and the primary invert in poorer rock mass with a defined RMR ranging from 27 to 32. The results indicate that displacements can be effectively controlled by defining the optimal distance between the excavation phases of the top heading and the primary invert. A detailed analysis of the collected data yielded a mathematical function relating displacement to the distance between the excavation of the top heading and the primary invert, which can serve as a tool for quick and straightforward correlation of displacements during tunnel excavation, considering the geological conditions present in the Kobilja Glava tunnel. Key words: tunnel, excavation, deformation, top heading, primary invert