Numerical investigation of a segmental grey cast iron tunnel ring: validation with laboratory data and application to field conditions

The structural response of a segmental grey cast iron (GCI) tunnel lining ring under distortion was investigated by means of finite element (FE) analysis. Building on previous experimental investigations, a 3D numerical model, capable of reproducing accurately the behaviour observed in the laboratory, was developed with the aim of providing guidelines for the structural assessment of GCI linings in engineering practice. A comprehensive validation of the segmental ring model with the laboratory data was first completed. Subsequently, a parametric study was conducted using a set-up that replicated the widely adopted elastic continuum method, so that differences between the numerical and the analytical solution could be attributed to the presence of the longitudinal joints. In this manner, the influence of the joints on the ring response was quantitatively established and recommendations for routine engineering calculations developed. A set of bending stiffness reduction factors are proposed as a function of the tunnel ovalisation, providing upper and lower limits of the bending stiffness, as well as a global reduction factor which is an average measure of the bending stiffness reduction. These factors can be integrated into the calculation procedure of closed-form solutions in order to account for the segmental nature of GCI linings