Investigation on the structural behaviors of segmental tunnel with a new generalized-beam-theory-based model incorporating cross-sectional distortions

Segmental tunnel lining structures constructed by Shields / TBMs are easily subjected to longitudinal settlement, cross-sectional torsion and flattening under complicated asymmetric loads or deformations. The existing soiltunnel interaction models typically discount the effect of cross-section torsion and flattening, which is proved to be considerable by field measurement. In the paper, a new generalized-beam-theory-based longitudinal beamspring model (GLBSM) for segmental tunnels is proposed considering four cross-sectional distortions (CSDs), including bending, shearing, torsion and flattening. The tunnel segments are regarded as beams with the four predetermined CSDs on Winkler foundation, and the circumferential joints are simulated by springs with four degrees of freedom stiffness. The methods to determine the joint stiffness are illustrated. Furthermore, the threedimensional soil reactions, elastic boundary conditions and the discontinuity of longitudinal ground are considered in the new model. The proposed method is verified with two case studies and compared with other published methods. Based on the new model, the flattening, torsion and assembly characteristics of the segmental tunnel are studied. Parametric analyses are performed to investigate the influence of critical variables on the structural responses of segmental tunnels, including the stiffness of circumferential joints, ground conditions, location of load and boundary conditions.