Vibration Influences on Shield Tunnel and Surrounding Environments Induced by Train Load on Line 5 of Tianjin Metro

This paper mainly discusses the problem of underground structure vibrations due to the Line 5 of Tianjin metro which passes under typical liquefiable silt layer. To better understand the vibration influences caused by trains to the surrounding environment and shield tunnel under different metro operating conditions, a series of field tests were conducted on a transition zone between a station and a shield tunnel. The tests obtained the operating conditions such as passenger loads and instantaneous speed of the trains passing through different measurement sections. The vibration acceleration responses of the rail sleepers, track slabs and tunnel walls were investigated in time and frequency domain. The results showed that the main frequency components of vibration source consist of two parts which are low part between 40 and 70 Hz and high part between 200 and 450 Hz. The vertical vibration responses at the rail sleeper and track plate were more sensitive to the train speed. Installing steel spring floating slab tracks (FST) and decreasing train speeds had obvious effects on controlling the level of vibration influence of the structures and surrounding environments. The results of this study can be used to resolve problems about environmental vibrations in metro design and to decide upon effective vibration countermeasures.