Abstract: The deformation of underground structure during earthquake is mainly controlled by the deformation of surrounding soil. Based on this idea, a simplified seismic analytical method, namely the boundary displacement method, was proposed for underground structure by applying soil deformation to the lateral boundary of soil-structure finite element model, while there is a lack of relevant experimental research. To explore the feasibility of the test method of applying pushover displacement to soil lateral boundary, a large-scale pushover test of soil-underground structure system was carried out taking the self-developed geotechnical comprehensive test model box as the test platform and the 1:10 scale Dakai station section tunnel as the research object. Response characteristics of underground structure and surrounding soil in the process of test were revealed based on the analyses of the strain, displacement, and stress. The results show that due to the strong nonlinear characteristics of soil materials, the inverted triangle deformation applied on the side of soil will attenuate in the transmission process, and the underground structure is subject to the coupling effect of shear deformation and extrusion deformation. The junction between central column and bottom plate is the seismic weak region in the whole structure. Horizontal coefficient of subgrade reaction is related to the level of soil displacement and the failure stage of structural side wall. The integral stiffness of structure is greater than that of the equivalent soil, and the ratio of lateral deformation between structure and soil is less than 1, which gradually increased with the increase of the pushing level. The soil-structure interaction could be quantified through deformation characteristic, which effectively fills the gap in the experimental study of soil structure interaction coefficient. The test method and conclusions have important guiding significance for seismic analysis of underground structure and feasibility study of pushover test.

Key words: underground structure, seismic performance, pushover test, boundary displacement method, soil-structure interaction