Behaviour of segmental tunnel lining under static and blast loads

Behaviour of segmental tunnel lining under static and blast loads. The scope of this thesis is to present an overview of the segmental tunnel lining subjected to static and exceptional loads such as blast pressure, taking into account different structural models in order to highlight the influence of joints. In chapter 2, the main parameters and characteristics of segmental tunnel lining have been described, analysing the geometry of precast concrete segments that form the ring and the different elements on their surface such as the guidance rod and gaskets and the behaviour of longitudinal and circumferential joints. Furthermore, in this chapter, the main properties of fibre reinforced concrete (FRC) have been presented in order to study the structural response for these types of segments. Chapter 3 focuses on the analysis of segmental lining under static loads in function of the construction phase until to reach the long term stability. The analytical methods and numerical methods have been briefly discussed, while the structural method has been described in detail because the structural response, in terms of internal forces and displacements, will be different in function of the assumptions on the behaviour of joints, on the acting loads during the final service stage and the interaction between the ground and tunnel lining. Chapter 4 pays attention to a general view of a design procedure for structures under blast loading and their response under this type of exceptional load. The scope of this chapter is to describe the blast loading categories, the phenomena of detonation and the main parameters in order to define the design time-history profile of a blast wave for unconfined and confined explosions. In Chapter 5, a case study of the Cross River Rail (CRR) project is presented. In particular, to replicate the geometry of the tunnel lining, two different types of 3D structural models have been carried out: continuous lining (Modified Usual Calculation Method) and segmental lining (Shell-spring Method). Both of them will be subjected to a static non-linear analysis and a dynamic non-linear analysis (with the presence of blast load) in order to take into account the different structural response in terms of solicitations and displacements. The results, obtained for static case, show that the bending moment and axial force of the continuous model are higher than the solicitation calculated for the discontinuous model (shell-spring model). This behaviour is due to the fact that the continuous model is stiffer than shell-spring model, by consequence the absence of joints on the lining reduces the overall deformation. Also for dynamic analysis it is possible to take into account similar considerations done for static analysis for both models and despite the displacements of lining subjected to blast load are low, the solicitations are very high compared with static loads also of 1 or 2 order of magnitude. Finally, in the last paragraph, it has been investigated the variation of internal forces and displacements of tunnel in function of ground stiffness for both models and the results show that when Young’s ground modulus increases, the values of bending moment, axial force and displacements decrease because when the stiffness of ground surrounding the tunnel decrease, the deformability of lining will be higher.