###### Abstract  
Shield docking technology is widely used in underwater shield tunnels. As the technology is not perfect, the instability of the tunnel face and the stress relaxation of segment lining caused by shield dismantling need to be solved. Using a cross-sea tunnel project, the segment lining reinforcement technology with steel channel in the process of shield docking is studied. The longitudinal stress relaxation effect of segment lining after thrust unloading is analyzed, and the theoretical solution of segment circumferential joint opening, with or without steel channel reinforcement, is derived. The accuracy of the theoretical model and the shell connector numerical model is verified by comparison. Then, the influence of key parameters, such as reinforcement range, steel channel quantity and steel channel model, on reinforcement effect is discussed. The results show that: (1) with the increase in the range of reinforcement, the maximum longitudinal displacement and the opening of the circumferential joints decrease first and then increase; (2) with the increase in the quantity and model of the steel channel, the maximum longitudinal displacement and the opening of the circumferential joints gradually decrease, and the reduction rate also decreases. The farther away from the shield tail, the weaker the reinforcement effect on segment lining. s +
Footnote †: journal: Applied sciences  
carelessness [6]. At present, some scholars have carried out relevant studies on segment lining structures [7; 8; 9; 10] and shield reinforcement technology [21; 22; 23; 24; 25; 26; 27; 28; 29; 30]. In the field of segment lining structures, the structural stiffness of the whole ring will change with \(k_{\Theta}\) and further affect the transmission and distribution of structural internal forces and deformation as well, which has been found through model shaking table tests and two-dimensional finite element dynamic analysis [7]. A simplified method for evaluating the moment carrying of a segmental tunnel liner that involves examining the influence of segmental joints, the number of segments and the soil subgrade modulus on the bending moment carrying characteristics of a segmental tunnel has been proposed [8]. The longitudinal stress relaxation characteristics of a shield tunnel in soft soil are studied via field tests [12]. The behavior of the load transfer mechanism of a shield-constructed tunnel in the longitudinal direction has been analyzed, and the distribution of stress and deformation in the tunnel lining was obtained. Additionally, the effects of circumferential and radial stiffness on the behavior of deformation and internal forces of tunnel lining have been discussed in detail [13]. An integrated framework based on laboratory experiments, real-time monitoring and statistical theory has been developed. As a case study, this presented method was employed in a typical underwater shield tunnel to prevent leakage disasters [16]. A risk assessment methodology that aims to evaluate the risks of the circumferential cracks of preexisting shield tunnels was proposed to ensure the security of existing tunnels under deep excavation during construction [17]. Considering the stratum with multiple discontinuities, a method was proposed to evaluate the longitudinal deformation caused by potential disturbance after shield tunnel construction, which can better predict the deformation characteristics of a shield tunnel, such as settlement, dislocation and the opening of joints [18]. When a shield tunnel is subjected to earthquakes and longitudinal deformation of the stratum, the segment ring may open along the longitudinal direction, and the tensile characteristics and failure modes of circumferential joints and bolted joints can be analyzed [19; 20].