Analytical approach for segmental tunnels considering nonlinear longitudinal joints in soft soils

Abstract

As a discontinuous ring structure, joints are the weakness of a tunnel lining, which have a significant influence on the tunnel deformations and internal forces. Since the deformations at the joints are discontinuous, joint behaviors are treated as nonlinear rotational springs. Besides, the tunnel-soil interactions are modelled as a series of radial and circumferential nonlinear Winker springs. Thereafter, an analytical approach based on the beam-spring model is proposed. The reliability of this method is verified with three cases available in the literatures. It indicates that the proposed method is reasonable to estimate the tunnel deformations. Furthermore, parametric studies are carried out to reveal the influence of the coefficient of earth pressure at-rest, the soil stiffness and local surcharge loadings on the tunnel responses. It has been shown that increasing the coefficient of earth pressure and soil stiffness is beneficial for reducing tunnel convergences. Under the earth pressures, cracks are most likely to appear at the crown, waist, and bottom of the tunnel. For the metro tunnel in Shanghai, when the relative local surcharge loading is larger than 0.3 (the corresponding convergence is about 14‰D, D is the tunnel external diameter), joints subjected to the negative moment are susceptible to reaching the ultimate state.