Normal and shear resistance of longitudinal contact surfaces of segmental tunnel linings

Stiffness of contact points has a significant effect on the internal forces and structural design of segmental lining of mechanically bored tunnels. Recent research on the effect of contact points in the structural analysis of segmental lining can be categorized into: (1) using hinges at contact points (HL model), (2) reducing liner rigidity (RR model), (3) using effective moment of inertia for liners (EMI model), (4) using rotational springs at contact points (BRS model), and (5) developing a comprehensive 3D model for segmenting contact locations. The present study tried to develop a precise contact model based on experimental direct shear tests (DST) on the concrete samples of contact points in segments. By selecting the normal stress between 0.25 and 2 MPa, about 90 tests were performed on the grooved cubic samples with and without gasket. As the practical outcome of this study, the contact shear and normal reaction moduli ks and kn were related to contact normal stress via two linear regression equations considering R2 of 99%. For evaluating the proposed method, finite element models of an urban tunnel liner were developed using the concept of beam on elastic foundation considering the proposed contact model of the present study (beam-contact springs (BCS)), the results of which were compared with those of the conventional contact models. Results demonstrated that the proposed model of this research had the highest correspondence with reduced RR, HL, EMI, BRS, and comprehensive coverage, respectively.