Creep behaviour of two-component grout and interaction with segmental lining in tunnelling

The complexity of the two-component grout behavior significantly affects the interaction between the support system and the tunnel. The loading of the filling material (and also of the segmental lining) takes place during the curing phase. At the end of it a creep phase develops which shows secondary deformations over time which result in a relaxation of the segmental lining and an increase in the deformation of the tunnel wall. In this work, a laboratory experiment campaign allowed to study the two-component material in detail during the creep phase. The typical trend of deformations over time, obtained for different stress load values and material curing age, was identified. The maximum stress was also evaluated which still allows to avoid the failure of the material over time, when a persistent state of stress is applied. The information obtained from the experimentation allowed to provide considerations on the support system-tunnel interaction, using the convergence-confinement method. The approach followed was then applied to a real case of a tunnel excavated in Northern Italy, for which it was possible to estimate the decrease in the load applied to the support system and the increase in deformations of the tunnel wall due to the creep phenomenon of the two-component material.