Experimental investigation on precast tunnel segments under TBM thrust action

An experimental procedure, useful for the evaluation of the structural behaviour of lining segments subjected to the Tunnel Boring Machine (TBM) thrust is presented in the paper. The study rises from the need to face the practical and rather frequent problem of cracks patterns in tunnels, occurring during the ring installation and in the first following phases of the TBM advance. This phenomenon, generally considered unavoidable, has a strong impact on the tunnel builder both in the economical and policy fields.The proposed set-up allows testing single segments under different loads, applied in different zones, in order to simulate the TBM thrusts, also in the curved stretch of the tunnel. Furthermore, different support conditions can be simulated, in order to account for the frequent situation of imperfect contact between the segments of two next rings.The experimental outcomes allow highlighting the different crack patterns related to the different support conditions, and appear useful for a deeper understanding of the segment behaviour under the TBM thrust