沉管隧道节段接头剪力键受力阶段与沉降控制标准研究

Load-Bearing Stages of Joint Shear Keys and Settlement Control Standards of Immersed Tunnel Elegments

当沉管隧道节段下部的地基由于荷载或地层因素产生差异沉降时,剪力键是抵制节段接头张开与扭转的主要受力构件,也是接头防水的重要结构保证。文章在1∶4.69大比尺模型试验和有限元三维数值模拟中,将差异沉降作为可变荷载,对地基差异沉降下的沉管隧道节段接头剪力键受力规律进行了研究。试验及分析结果表明:在纵向与横向差异沉降下,沉管隧道节段接头剪力键的受力过程可以分为三个阶段。第一阶段为剪力键榫与剪力键槽间的缝隙及橡胶垫初步压缩阶段,应力增长速率较低;第二阶段为剪力键充分受力阶段,应力增长速率较高,当差异沉降达到一定量值后,节段接头会通过局部挤压或摩擦的方式帮助剪力键受力;第三阶段,剪力键进入屈服状态,此时剪力键仍能够继续受力,但已有微裂纹产生。根据剪力键在正常使用极限状态下的剪力值,所确定的沉管隧道节段允许纵向与横向差异沉降值分别为11.5 mm和11.1 mm。建议在沉管隧道沉放完成后,保留部分顶、底板位置的拉索,以提高节段接头剪力键的结构安全。

Shear keys are the main load-bearing components for resisting expansion and rotation of elegment joints and are a structural guarantee of joint waterproofing when differential settlements of foundations occur because of load or soil layer factors. Therefore, differential settlements were taken as the variable loads in 1 ： 4.69 large-scale model tests and 3D FEM numerieal simulations to study the load-bearing laws of shear keys on elegment joints affected by differential settlements. The test results show that the load-bearing processes of shear keys can be divided into three stages under the effects of longitudinal and transverse differential settlements. In the first stage, gaps and rubber pads between the shear keys and their grooves start to be compressed, and the stress growth rate is relatively small. In the second stage, shear keys undertake loads effectively and the stress growth rate is much larger, comparatively, while the elegment joints help the shear keys undertake loads through local compression or friction when differential settlements reach a certain extent. In the third stage, shear keys are inclined to yielding, and though shear keys can still bear more loads, micro-cracks occur. Based on the shearing forces of shear keys in the limited state of normal use, the longitudinal and transverse allowable differential settlements of elegments are determined as 11.5 mm and 11.1 mm, respectively. It is recommended that several prestressed cables on the roof and floor of the elements remain after immersion in order to improve the structural safety of the shear keys.