ABSTRACT
This paper investigates the effect of constructing a new circular (cross-passage) junction tunnel, perpendicularly intersecting existing deep circular (twin) main tunnels, in rockmass, excavated with full-face conventional method and supported with shotcrete lining, via parametric 3D numerical analyses, by varying the diameter of the main and junction tunnels, the overburden height, the strength and deformability of the surrounding rockmass. The analyses focus on the distribution of the circumferential and longitudinal bending moments developing at the primary support of the intersection areas and quantify the interaction effects by comparing the bending moments at the primary support of the main tunnels before, during and after the construction of the junction tunnel. The results of the analyses are used to produce normalized graphs accompanied by analytical equations for the bending moments acting on the intersection zones between the main and the junction tunnels, applicable for preliminary estimations of primary support requirements at tunnel junctions.
