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.

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