沉管隧道管节接头剪切破坏试验

为了研究沉管隧道最薄弱的环节-接头的受力特点和破坏机制，根据实际沉管隧道接头形式开展了1：4大比例尺的沉管隧道接头低周往复加载拟静力试验。试验模型由2节钢筋混凝土管节组成，接头主要由钢筋混凝土剪力键和橡胶填塞垫构成，为贴近实际工程结构反应，试验模型采用与实际工程相同强度的钢筋和商品混凝土。利用顶杆位移计和拉线位移计等传感器得到了试验模型在循环剪切荷载作用下的接头破坏机理，并分别从沉管隧道试验模型的荷载-位移滞回曲线、接头抗剪承载力、接头与管段刚度比3个方面对试验结构进行了分析。试验结果表明：橡胶填充垫对沉管隧道接头具有缓冲保护作用；低周往复荷载下沉管隧道接头主要经历橡胶垫弹性变形、橡胶垫与剪力键协同作用及剪力键塑性变形3个阶段；接头总抗剪承载力为674 kN（3个单键的抗剪承载力分别为417，320，417 kN），接头抗剪能力并不是单个剪力键承载力的线性叠加，需考虑剪力键之间的协同作用；接头与管节的剪切刚度有效比为1/960~1/672，接头是抗震的薄弱环节，在受到地震荷载时，变形主要集中在接头部位，并主要由接头处剪力键承担；接头的破坏模式主要体现在剪力键凸榫的端部剪裂及其失效后接头的不可恢复性变形。

Experimental Failure Analysis on Immersed Tunnel Joint Subjected to Shear Loading

A quasi-static test of an immersed tunnel model (based on the features of an actual immersed tunnel structure) under low cycle loading was conducted to study the mechanical characteristics and failure modes of the immersion joint, which is the weakest part of an immersed tunnel. The reduced-scale ratio of the tunnel model was 1：4. The testing model contained two tunnel segments, and the joint was mainly composed of reinforced commercial concrete shear keys and rubber infilled pads. Based on the similitude analysis of the immersed tunnel structure and the actual structure, the tunnel model segments were prefabricated with reinforced commercial concrete of the same strength as that used in the actual project. The joint deformation and failure mechanism were obtained from the test using displacement meters. The model responses were analyzed from three aspects: load-displacement hysteretic curve, shear strength, and stiffness ratio between the joint and tunnel segment. The results indicate that the rubber infilled pad provides a protective buffer effect to the immersion joint. The immersion joint undergoes three stages (the elastic deformation stage of the rubber infilled pad, synergistic stage between the rubber infilled pad and the shear key, and plastic deformation stage of the shear key) under low cycle loading conditions. The shear resistance capacity of the immersed tunnel joint reaches 674 kN (the shear resistance capacity of three single shear keys are 417, 320, and 417 kN, respectively). The shear resistance capacity of the immersion joint is the synergistic effect of three shear keys rather than their linear superposition. The effective shear stiffness ratio between the joint and immersed tunnel element is 1/960-1/672. The immersed tunnel joint is the vulnerable part of an immersed tunnel, in terms of anti-seismic design. When subjected to earthquakes, deformation is mainly concentrated in the joint, and the shear keys mainly bear the deformation. The failure in the root of the shear key tenon and the unrecoverable deformation of the joint are regarded as the main failure modes of an immersion joint.