VERTICAL RANDOM VIBRATION MODEL FOR SUBWAY SHIELD TUNNEL IN SOFT SOIL

In the allusion to the Chinese common types of a subway shield tunnel and a bolster-embedded monolithic-track bed, a vertical random vibration model for a subway shield tunnel in soft soil is established on the basis of vehicle/track coupling dynamics and the nonlinear expression between dynamic stiffness and dynamic strain of soft soil. The model can be used to research the influence of the nonlinear dynamic stiffness of soft soil on the random vibration of a shield tunnel. The results show that when the dynamic stiffness of soft soil nonlinearly varies with its dynamic strain, the random vibration of a shield tunnel would has a descending trend in the frequency band higher than 10Hz, whereas it would not descend but rise below 10Hz. And the declining extent of the random vibration of a shield tunnel above 10Hz is obviously less than its rising extent for 10Hz below. In addition, from the view of the amplitude-frequency characteristics of foundation reactions under a shield tunnel, the nonlinear variation of the dynamic stiffness of soft soil not only affects the frequency-domain amplitudes of foundation reactions, but also gives rise to the redistribution of their amplitudes in a frequency domain, especially below 10Hz.