ABSTRACT: This paper describes an evaluation of the optimum number of reinforced concrete segments per ring that can best fulfil the tunnel lining function to support the design loads. Hence, the effects of number of segments in the ring were investigated among which the worst case has been selected for further investigation. Subsequently, the influence of Key-segment location has been considered in-depth. To construct the required models, the beam-spring concept has been employed. The required input data was obtained from Line-4, Tehran subway tunnels. Abaqus, a finite element program, was used to analyze the problem. This program has the capability of analyzing tunnel structures by considering the effect of two-dimensional rotational behavior of intersegmental joint condition. The results demonstrate that as the number of segments per ring increases, the corresponding maximum bending moment within the lining system decreases. Consequently, the related displacement due to the lining flexibility increases. Finally, it has been concluded that due to increase of the number of segments per ring, the importance of position dependency of the Key-segment within the lining system is significantly reduced.
Shield tunneling has become a widely-used method, in particular, for urban and suburban tunnel construction due to its superior performance compared to conventional methods. The method attributes negligible effect on surrounding environment, fast and safe construction, and outstanding performance in earthquake resistance. (Nadimi et al. 2010 and 2011, Zhang et al. 2004). The arrangement and number of segments in Shield tunneling may differ based on the existing situation; however, the entire assembling process is generally the same (Chen and Mo 2006). The design of the precast segmental lining is based upon the proposed tunnel alignment and the expected geological and hydrogeological conditions at the tunnel level. The existence of joints in a tunnel ring will influence the behavior of the support system and the induced stress pattern in the linin. Actually, inter-segmental joints can be used for the force and lining behavior evaluation. The segmental joint will have a behavioral mode somewhere between a total fixation and a hinge (Majdi et al., 2010, Nadimi and Shahriar, 2013). The orientation of joints within each segmental ring may vary along the tunnel route depending on the tunnel boring machine steering alignment. Furthermore, the possible mode of the joint orientation is governed by the joint numbers. The combination of these two factors might influence the stresses induced in the tunnel lining. Accordingly, both cost and planning purpose might be affected (Hefny and Chua, 2006). Therefore, the main purpose of this research is to investigate the influence of joint numbers and their orientations on the tunnel lining behavior. However, the tunnel lining design is almost based on empirical and analytical methods like the “beam spring model” which was proposed to analyze the tunnel lining under the ground loads (Murakami and Koizumi 1978). This method has become the standard technique to design shield tunnel lining in Japan (JSCE 1996). In this study, the model was used for representing the segmental joints and surrounding ground as rotational springs and non-tension ground springs, respectively.