Using a novel small-scale model to investigate mechanical behaviours of full-scale shield tunnels

A novel small-scale model was proposed to investigate the mechanical behaviour of full-scale shield tunnels. Because it used fine-aggregate grout, model dimensions could be significantly scaled down, giving cost advantages. Although small, most structural features of practical shield tunnels, including bolts and steel reinforcements, were retained. Independently designed casting moulds allowed high-accuracy manufacture. Verification loading tests were conducted to assess the proposed model. Both deformation and failure generally agreed with full-scale experiments. Complex loading tests were then performed to study shield tunnel response under unilateral unloading and soil arching. Results showed that horizontal unloading can be much more adverse than vertical unloading and deserves special attention, because a shield tunnel usually first exhibits horizontal ovalling deformation after construction due to overburden pressure.