封顶块位置对高水压通缝拼装管片结构的影响

为了探明封顶块位置对盾构隧道管片结构力学行为的影响，基于苏通GIL （gas-insulated transmission）综合管廊隧道工程，选取封顶块在拱顶和拱腰两种代表性工况，开展了高水压条件下的通缝拼装管片结构原型试验，从管片结构的变形、受力、裂纹开展情况和最终破坏状态等方面对两种工况的试验结果进行分析. 研究结果表明:不同封顶块位置对管片结构的影响总体表现为对结构整体刚度的削弱不同，其形成的刚度削弱区域抵抗指向洞外变形的能力要强于指向洞内变形的能力；封顶块位于拱腰时结构整体刚度更大，管片结构椭圆度和单点最大位移均分别减小了39.8%和38.2%；封顶块位于拱顶时结构抗弯刚度削弱明显，易出现较大的纵缝张开，而封顶块位于拱腰时管片最大纵缝张开量明显减小，仅为前者的53.3%，且连接螺栓受力减小了54.4%；封顶块位于拱腰时，管片环拱底内弧面更容易产生裂纹、开裂荷载相对更小，管片内部主筋更早进入受拉状态；封顶块位于拱顶时管片结构由于纵缝张开量较大，在较高水压的情况下破坏始于纵缝处混凝土的压剪破坏进而导致的结构失稳. 

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.