Experiment on stiffness ratio of immersion joint to immersed tunnel element

Aimed at the problems in taking the value of relative stiffness ratio of the immersion joint to the immersed tunnel element, which is neither formulated analytical solutions, graphs nor experimental data are available, based on the configuration characteristics of the immersion joint and the tunnel element, an experiment on the mechanical behavior of the immersion joint with geometry of 1:10 was designed. The compression curve, moment-rotation curves and shear force-shear displacement curves of the joint subjected to different levels of axial force were obtained as well as stiffness ratio curves of the immersion joint to the tunnel element under the axial, flexural and shear loads in the joint. The fitting curves for the three types of stiffness ratio curves were obtained and analyzed respectively. The relationships between the stiffness ratios and the axial force were discussed. The results show that, the axial stiffness ratios under the loading and unloading condition are not similar, the axial loading stiffness ratio is larger than the axial unloading one and both of them show a linear increasing trend; with the increase of the axial force, both the flexural and the shear stiffness ratios also experience a linear increasing trend. In the service hydraulic pressure range of the joint (corresponding to the axial force from 440 to 1 760 kN), the ranges of the axial loading, axial unloading, flexural and shear stiffness ratio are 1/360 to 1/120, 1/1 028 to 1/305, 1/1 161 to 1/25, and 1/76 to 1/24 respectively. Compared to axial and flexural stiffness ratios of immersion joint to immersed tunnel element, shear ratio is relatively large and less sensitive to the change of the axial force.