Deformation mechanism and control technology of segment joints during process of shield tunneling prior to shaft excavation in a heat-supplying tunnel project

The shaft excavation following the shield tunnel is an efficient and economic method in the construction of heating shield tunnel. Based on the first large cross-section heating shield tunnel project, the stress characteristics and deformation mechanism of segment joints at different construction stages are analyzed using the longitudinal equivalent continuous model and the elastic foundation beam theory, and the control measures are proposed. The numerical model for the full face interface element is established, and the control effect of the measures is analyzed and appraised. Finally, the change laws of longitudinal stresses and segment joints at different construction stages are measured through field monitoring. The results indicate that the deformation of segment joints can be divided into two stages in the shaft excavation following the shield tunnel: foundation excavation and segment removal, and the segment removal is the main reason. The negative bending moment formed in the excavation of shaft affects the bottom segments of tunnel, and the disappearing of remnant shield force caused by segment removal enlarges the loss of longitudinal stress and opening of segment joints. According to the monitoring results, the control measures including longitudinal tension segment and retightening the bolt, pouring concrete in the tunnel bottom and secondary grouting behind the lining can effectively control the loss of longitudinal stress, and reduce the deformation of joints. The maximum opening of segment joints is 3.51 mm, meeting the waterproof requirements of tunnels. The numerical model based on the full face interface element can be used to simulate the mechanical behaviors of the segment joint in construction, and the results can be used as reference for evaluation of the control effects.