Computational evaluation of strains measured in tubbings of a segmental tunnel lining

Abstract

The Koralm tunnel is a railway tunnel in the south of Austria. The segmental tunnel lining rings in construction lot KAT3 consist of seven prefabricated reinforced concrete tubbings. So-called measurement rings are equipped with 38 embedded vibrating wire strain gauges. They measure the normal strain in circumferential direction. The present work is focused on the strain data from nine measurement rings. They are located close to each other in a geologically interesting area near the Lavanttal fault system. The evaluation of the monitoring data includes computation of the normal stresses in both the circumferential and driving directions, as well as quantification of the utilization degree of the tubbings. This is done by considering the long-term viscoelastic behavior of mature concrete within the framework of a hybrid, i.e. computational-experimental, approach developed by Razgordanisharahi et al. [12]. Thereby, normal strain histories measured inside the tubbings are translated into stress histories using an integro-differential viscoelastic model. It is based on the assumptions of a plane strain state in the tunnel cross-section planes and a plane stress state in the planes parallel to the tangential plane of the midsurface of the tunnel lining. The utilization degree of concrete surrounding the vibrating wire strain gauges is determined using the Drucker-Prager failure criterion. The largest utilization degree determined in any tubbing is taken as the utilization degree of that tubbing. The central result of the present work is the visualization of the development of the utilization degrees in the nine measurement rings over the first two years after the start of structural monitoring. At the end of the evaluation period, the largest utilization degree of the measurement rings is approximately 42 %.