Abstract: Excessive ovalization deformation of shield tunnels causes reduced structural durability and increased operational safety risks. To address this challenge, an insitu experimental study is conducted on tunnel deformation repair induced by internal pressure loading using the internal loading test platform for shield tunnels. The mechanical response characteristics of the tunnel structure under different burial depths are systematically analyzed. The experimental results show the following: (1) Vertical internal pressure loading exhibits a favorable deformation repair effect on shield tunnels with transverse ovalization deformation. At a burial depth of 3 m, an internal pressure of 550 kN restores the tunnel ovality to 6‰; at a burial depth of 5 m, an internal pressure of 1 330 kN achieves the same level of recovery (6‰). The recovery rate of transverse deformation is significantly lower than that of vertical deformation. (2) When the internal pressure reaches 1 000 kN, compared with the 3 m burial-depth condition, the 5 m burial-depth condition exhibited a maximum reduction of 75% in joint-opening recovery, while the variation amplitudes of bolt axial force and segment surface strain at the corresponding locations decrease by 88.6% and 53.3%, and a 68.9% decline in deformation-repair efficiency. These results demonstrate that greater burial depth leads to a lower degree of tunnel deformation recovery and lower repair efficiency. (3) During the repair process, the bolt axial force and surface strain at the crown show the largest variation amplitudes, with the amplitude of bolt axial force change being 33.3% higher than that of segment surface strain change. The structural load is primarily carried by the bolts, while the segments mainly undego rigid-body displacement. In the crown region, the axial force gradually decreases and the bending moment increases, whereas near the standard block B1 (135°) and the key block K (243°), the axial force gradually increases and the bending moment decreases. The axial force and bending moment variations are most pronounced at the crown, with the amplitude of axial-force change being 11.7% higher than that of bending-moment change. This indicates that axial-force redistribution plays a dominant role over bending-moment adjustment in restoring the geometric shape of the tunnel.

Key words: shield tunnel, ovalization deformation, internal pressure loading, insitu test, mechanical response