3D modelling of concrete tunnel segmental joints and the development of a new bolt-spring model

In a segmental metro tunnel, it is widely observed that cracks, water leakage and other structural defects usually appear at segmental joint section of a smaller stiffness than main tunnel segment section. In this study, a 3D finite element analysis was conducted to simulate a typical concrete segmental joint explicitly using 3D continuum elements, and the performance of 3D continuum model was validated against laboratory tests available in literature. Since such continuum model may cost excessive computational time when a large-scale tunnel structure is analysed, a new bolt-spring model was developed to simplify the structural features of concrete segmental joint. In the bolt-spring model, the interaction between bolt and segment was modelled by a set of normal springs and shear springs: the stiffness of the normal springs is mainly determined by the bolt itself, whilst the shear springs take account of bolt-segment friction, interaction and shear resistance of the bolt. In the meanwhile, the interaction between two adjoining tunnel segments is explicitly modelled using contact elements. The proposed bolt-spring model is able to simulate the details of joint deformation and contact pressure between segments more realistically than previously available by conventional methods (e.g. continuous ring, beam-spring model (BSM)), where segment-segment interaction is not explicated modelled. Compared to the continuum model, the bolt-spring model saves up to 90% computational time without compromising numerical accuracy. Furthermore, this paper compared the mechanical behaviour of a concrete joint against that of a cast-iron one with particular emphasis on the development of different bolt-spring models.