Research on segmental model container and its validation for multi-point shaking table test of long tunnels

Aimed at the problems that the seismic analysis of long tunnels subjected to non-uniform seismic loadings is limited to analytical derivation or numerical analysis, lacking effective experimental or field data, the critical issue for multi-point shaking table test is how to accomplish a practical continuous and non-uniform excitation over a long tunnel by a number of discrete shaking tables. A segmental model container for multi-point shaking table test to simulate long tunnels was developed, using four independent shaking tables worked in coordination as a large linear shake table array. The segmental model container was developed not only to hold the model soil and the model tunnel but also to realize the equivalent transformation from discrete multi-point shaking of the tables into continuous non-uniform seismic excitations. The challenge to develop the container was the design of the dimension of model container and the connection between each of its components. The optimization objective was to make the peak acceleration response and the dominant frequency of an inactive box coincided with those of the active box, and to leave a reasonable time lag between adjacent boxes to reflect the wave passage effect along the vertical direction of the model container. Based on analytical solution and numerical analysis for multiple loading conditions, the optimization design of dimension (40 m length×4.5 m width×1.2 m height) of the segmental model as well as the connection method (elastic hinge) between each of its components was finally obtained. A series of multi-point shaking table tests for the segmental model container were conducted to investigate the non-uniform seismic excitation effect along the longitudinal direction. The results show that the developed model container can be used to effectively realize the equivalent transformation from the four independent shaking tables into continuous multi-point non-uniform seismic excitations, which fully reproduces the spatially varying seismic motion and therefore the validity of the designed model container is verified to be used in multi-point shaking table test of long tunnels. This research results provide a reference for the multi-point shaking table tests of long tunnels.