Experimental study on the mechanical behavior of segmental joints of shield tunnels strengthened by a steel plate-UHPC composite

This research proposed a new technology to strengthen segment joints in shield tunnels based on steel plateUHPC composite. In order to understand the strengthen mechanism of the steel plate-UHPC composite on the segmental joints, full-scale experiments were conducted to study the characteristics of the strengthened joints, including deformation, crack development, interface behavior, stress distribution, and the failure process. The results demonstrate that the deformation process under sagging moments involves four stages: elastic deformation, elastic-plastic deformation, debonding, and failure, whereas under hogging moments, the deformation can be summarized into three stages: elastic-plastic deformation, debonding, and failure. The use of UHPC strengthening facilitates more extensive crack development, and promotes uniform stress distribution within the concrete, with efficient utilization of material properties. The presence of anchor screws maintains a certain level of ductility after interface debonding. A significant improvement in the ultimate bearing capacity and flexural stiffness of specimens was observed with the use of steel plate-UHPC composite. The ultimate bearing capacity of initially strengthened specimens under sagging and hogging moments is increased by 503.3% and 72.2%, respectively, and the flexural stiffness is increased by 177.9% and 3803.2%, respectively. Moreover, the predamaged state of the strengthened specimen exhibits a significant increase in ultimate bearing capacity and flexural stiffness under a sagging moment, while remaining basically unchanged under a hogging moment.