Experiment on Co-deformation and Stress Characteristics of Through-joint Assembled Segments under Concentrated Force

To establish a theoretical basis for deformation control in the design and construction of near-joint assembled shield tunnels, and to advance beyond traditional model testing approaches, this study independently developed a novel model testing method. This method integrates loading devices, model segments, confining pressure calculation, and a monitoring system. Model tests on near-joint assembled shield segments were conducted. The results preliminarily indicated that under a single-point concentrated load, the longitudinal deflection deformation of the tunnel, the circumferential joint misalignment, and the convergence deformation were approximately linearly and positively correlated. Under graded loading, the misalignment of each longitudinal joint in the loaded ring and the odd-numbered rings gradually decreased clockwise from the loading point at the arch bottom. The distribution characteristics of the reaction forces on segments within each ring were largely consistent. The magnitude of segment reaction forces followed the order: 270° > 202.5° > 135° > 22.5° > 337.5° > 67.5°, with the maximum reaction force located at the left arch waist. The strain at the center point of the inner arc surface of each segment exhibited distribution characteristics and a development law similar to those of the segment reaction forces. The strain of segments at the same position in each ring approximately followed a normal distribution along the longitudinal direction. Therefore, when the stress at the center point of each segment in the loaded ring is known, the internal forces of segments in each ring under a single-point concentrated symmetrical load can be calculated. This testing method is not only applicable to mechanical research on shield tunnels with various assembly methods but also, compared to tests on tunnels in soil, allows for more intuitive observation of test phenomena and results. Furthermore, it enables dynamic adjustment of displacement monitoring elements, making monitoring more convenient.