Abstract: Improving the seismic capacity of the underground utility tunnel project is of great significance to the sustainable development of the city. Taking the actual engineering as the background, a three-dimensional structure-soil model of the underground utility tunnel with different lengths is established. Based on the modal analysis, the Rayleigh damping method is used to analyze the time history of the model. The correlation method is used to analyze the influence of the model's aspect ratio on the calculation accuracy of the model and the influence of the wall thickness on the mechanical properties of the structure is studied. The research results show that: 1) When the aspect ratio is less than 1:1, the stiffness of the model is small, resulting in large errors; when the aspect ratio of the model is 1:1~10:1, the analysis results are relatively stable; when the aspect ratio reaches 12:1, the modal analysis result is dominated by rigid displacement; 2) For the analysis model that only needs to obtain the maximum response of the structure, the aspect ratio should be 1:1; 3) The structural stress is mainly controlled by the bending moment; the largest area of the main stress of the structural bending moment is concentrated in the surrounding corner areas; in actual engineering, the corner areas should be strengthened; and 4) As the wall thickness increases, the seismic load on the structure increases, but at the same time the maximum principal stress and the inter-story displacement angle decrease. Taking into consideration both safety and economic factors, the wall thickness should be 250mm.

Key words: utility tunnel, seismic resistance of underground structure, modal analysis, time-history analysis