Convergence Predictions and Primary Support Optimization of the Tunnel Progon

Abstract

The tunnel Progon is being constructed as a part of Corridor 10 highway project about 5 km north from the border crossing with Bulgaria in southern Serbia. During the design process 2D finite element analysis was utilized with the objective to investigate an influence of different support systems on the convergence across an excavation. Two models were used in calculations. The first model is elastic perfectly-plastic with constant stiffness independent of the stress level. The second model assumes hyperbolic relationship between the deviatoric stress and axial strain and stress dependent stiffness. This model also accounts for small strain stiffness of soil. In order to allow for a certain convergence across an excavation the load reduction method was utilized. Convergence monitoring is currently ongoing for the excavated portion of approx. 700 m of the tunnel exit portal. The measurements show cumulative displacements in the range of 1-3 cm. Results obtained by the analyses prior to the tunnel construction are in good agreement with the measurements. Convergence is approx. 5 cm when MC model is used and around 1 cm in the case of HS-small model, thus limiting the measurement results from the lower and upper bound.