SUMMARYThis paper proposes a numerical approach to the hyperstatic reaction method (HRM) for the analysis of segmental tunnel linings. The influence of segmental joints has been considered directly using a fixity ratio that is determined on the basis of the rotational stiffness. The parameters necessary for the calculation are presented. A specific implementation has been developed using a FEM framework. This code is able to consider the three-dimensional (3D) effect of segment joints in successive rings on the tunnel lining behaviour. The present HRM allows one to take an arbitrary distribution of segment joints along the tunnel boundary into consideration. In addition, the rotational stiffness of segment joints has been simulated using nonlinear behaviour, as it is closer to the true behaviour of a joint than linear or bilinear behaviour.The numerical results of three hypotheses on ring interaction, which allow the 3D effect of a segmental tunnel lining to be taken into account, have been compared with data obtained from the shield-driven tunnel of the Bologna-Florence high-speed railway line project. The numerical results presented in the paper show that the proposed HRM can be used to effectively estimate the behaviour of a segmental tunnel lining.
One of the most important factors in the design of a segmental tunnel lining is the influence of the segmental joints on its overall behaviour. In this study, a reduction factor has been applied to the bending rigidity of the segmental tunnel lining. An improved numerical hyperstatic reaction method (HRM) is presented in this paper in order to study the behaviour of the segmental tunnel lining. The necessary parameters for the calculation are presented. A specific implementation has been developed using a finite element method framework. A comparison between the results obtained using the HRM and those of a numerical model has been made that allows the HRM to be validated. Extensive parametric analyses have been conducted to estimate the segmental tunnel lining behaviour for several cases, in order to cover the conditions that are generally encountered in excavation practice.
During the construction of twin tunnels excavated in close proximity to each other, the prediction of the influence of a new tunnel construction on an already existing one plays an important role in the design and construction of the tunnels. The researches in the literature indicate that this influence depends to a great extent on the distance between the tunnels. However, most of the reported cases in the literature on the mechanized excavation of twin tunnels have focused on the effects of the relative position between the two tunnels on surface settlements. Some of them have dealt with the behaviour of the tunnel structure through the use of simplified numerical models. The numerical investigation performed in this study, using the FLAC 3D finite difference code, has made it possible to predict the impact between tunnels using full three-dimensional simulations, in which most of the elements of a mechanized tunnel process have been modelled. The effects of tunnel distance on the structural forces induced in both tunnels, and the displacements in the surrounding ground have been highlighted. A modification has been made to the superposition method to predict the settlement surface trough over twin tunnels.
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