Mechanical properties of segmental joints strengthened by assembled reinforcement structures for shield tunnel linings

We develop assembled reinforcement structures (ARSs) composed of connection parts, connecting rods, and straight bolts to strengthen segmental joints in the lining of shield tunnels. Through full-scale bending experiments and numerical simulations, we investigate the deformation and failure characteristics of segmental joints strengthened by ARSs, and propose a novel optimization method for ARSs. The experimental results show that the ARSs can effectively limit the opening of a segmental joint, but also that separation can occur during loading if the connection between the ARSs and segments is not designed properly. Importantly, this connection can be improved by embedding anchor parts in the concrete. In numerical modeling, we investigate the failure modes of segmental joints strengthened by ARSs for both positive bending and negative bending loading cases. In the case of positive bending loading, first the concrete around the anchor parts cracks, and subsequently the concrete on the external side of the joint is crushed. The joint failure is caused by the crushing of concrete on the external side of the joint. While the un-strengthened segmental joint fails with an opening of 5.884 mm, the strengthened segmental joint only opens by 0.288 mm under the same loading, corresponding to a reduction of 95.1%. In the case of negative bending loading, the concrete around the anchor parts first cracks, and then the amount of joint opening exceeds a limiting value for waterproofing (6 mm), i.e., the joint’s failure is caused by water leakage. While the opening of the un-strengthened segmental joint is 9.033 mm and experiences waterproofing failure, the opening of the strengthened segmental joint is only 2.793 mm under the same loading, corresponding to a reduction of 69.1%. When constructing a new shield tunnel, anchor parts could be embedded in the concrete segments in tandem with ARSs for improved resistance to joint opening. For existing shield tunnel linings, anchor parts cannot be embedded in the concrete segments; therefore, the connections between the ARSs and concrete need to be optimized to strengthen the segmental joint.