THREE- DIMENSIONAL MODELING OF A TUNNEL INTERSECTION AND ITS EFFECT ON LINING DISPLACEMENTS AND INTERNAL FORCES (CASE STUDY: HAKIM TUNNEL -TEHRAN)

highway-Iran. The tunnel has three lines on each side, each of which consists of two distinct pathways. The modeling has been done using finite-element software ABAQUS. An elasto -plastic model with Mohr-coulomb failure criteria was used to present the stress-strain soil and an elastic model was considered for shotcrete behavior. The NATM tunneling method was considered in numerical analyses. Extreme care taken during excavation and immediate application of support media prevent unnecessary loosening of media. The effect of elasticity coefficient, which increases with depth, was also considered. Due to the excavation of the child tunnel, the surface settlement over the intersection area and deformation of crown intersection were studied. Results showed that the upper area of shotcrete in the main tunnel, near to intersection, and near to the side's area in the child tunnel, is a critical section for designing the support. In order to verify the accuracy of finite- element model, some results are compared with field measurement. The results showed that creating an opening in the main tunnel causes the surface settlement increase to 29%. The results showed that with opening of the main tunnel, moments and axial forces in the tunnel lining significantly increase. In the circumferential direction, half of the section close to the opening was more heavily affected than the other part. In the longitudinal direction, the lengths of the scopes of influence were about 1.5 times the diameter of the child tunnel. Also, the results showed that by an increase in the coefficient of lateral pressure, moments and axial force increase only in the area of two tunnel junctions. It is proposed that local thickening combined with an improvement in the bearing capacity should be undertaken to increase the stability of the intersection.