Multi-point shaking table test simulation and analysis of a super-long immersed tunnel

In order to investigate the response of immersed tunnel under non-uniform seismic excitation, taking the Hong Kong-Zhuhai-Macao Bridge under construction as background, the multi-point shaking table tests were conducted to simulate the super-long immersed tunnel based on linear multi-function shaking table system which contains 4 shaking tables. According to the scale of the super-long immerse tunnel engineering and the characteristics of multi-point shaking table system, the relationships of similitude ratios of soil and structure powers required by the test were investigated. Besides, segmental model box was designed and manufactured for the simulation of non-uniform seismic input along the axial direction of the tunnel. The connected model boxes, with entire length of 40 m, contained 4 active model boxes and 8 inactive model boxes. By conducting discrete multi-point shaking table test of model boxes under non-uniform excitation, the transition from discrete multi-point input mechanism to consecutive input mode by the segmental model boxes was verified. The optimal mixture for model soils was tested and determined via the laboratory dynamic tri-axial shearing experiments. Based on the similitude analysis of both the structural inertial force and the relative stiffness ratio between soil and structure, several materials were selected and the segments of immersed tunnel were prefabricated with aluminum alloy. 98 tunnel segments were used in the test, with size of 600 mm (length) × 375 mm (width) × 170 mm (height), reaching 36.75 m in entire length. Silicone rubber piece whose mechanical properties are similar to those of rubber was selected to simulate the GINA rubber water stop in the tunnel tube joint. Through multi- point shaking table tests simulations under working conditions, the seismic response law of the immersed tunnel under non-uniform excitation was obtained systematically. Through the data analysis under various working conditions, acceleration of field and tunnel pipe and change conditions of tunnel element joints were obtained. Data of longitudinal acceleration response of structure showed obvious effects of wave passage. The results show that, displacement of tunnel element joints is smaller than the allowance values under ODE, MDE and RDE test cases, which indicates that the structure is in the safe state.