Effect of Key Block Position on Straight Assembling Segmental Lining Structure under High Water Pressure

In order to find out the influence of the key block position on the mechanical behavior of the segmental structure of a shield tunnel, based on the Sutong GIL （gas-insulated transmission） integrated pipe gallery tunnel project, two typical working conditions, i.e., the key block being located at the vault and the waist, are selected to carry out the prototype test of the straight assembling segmental lining structure under high water pressure, and the test results in the two conditions are analyzed from the deformation, stress, crack development and final failure state of the segmental structure. The results show that the influence of different position of key blocks on the segmental structure is generally manifested in the different weakening of the overall stiffness of the structure, and the stiffness-weakening area formed has a stronger ability to resist the deformation outside the tunnel than that inside the tunnel. Compared with the key block at the vault, when the key block is located at the arch waist, the overall rigidity of the structure is greater, the ellipticity of the segmental structure and the maximum single-point displacement are reduced by 39.8% and 38.2%, respectively. When the key block is located at the vault, the bending stiffness of the structure is weakened obviously, and the large longitudinal joint is easy to open; while when the top block is located at the arch waist, the maximum longitudinal joint opening of segment is reduced obviously, which is only 53.3% of the former, and the force of the connecting bolt is reduced by 54.4%. In addition, when the key block is located at the arch waist, the arc surface in the bottom of the segmental structure is more prone to cracks, the cracking load is relatively smaller, and the main reinforcement inside the structure enters the tension state earlier; when the key block is located at the vault, the longitudinal joint opening of the segmental structure is large, and the structural instability is caused by the compressive shear failure of the concrete, which starts from the longitudinal joint in the case of high tensile force.