Abstract:  To develop a rapid detection method to study the local disengagement in metro monolithic track bed, the HilbertHuang transform (HHT) is applied to the sensitive vibration responses obtained before and after the local disengagement of the monolithic track bed. Subsequently, crucial information is extracted from the transform spectrum to identify the location of local disengagement. The results reveal the following. (1) The vertical accelerations of the carriage, bogie, and track bed are most sensitive to the local disengagement in the monolithic track bed. (2) By applying the HHT to the three kinds of vertical accelerations, it is observed that it is difficult to use the HHT spectrum of the vertical acceleration of the track bed to identify the local disengagement of the monolithic track bed, but that of the carriage and the bogie varies significantly near the local disengagement region. The length of local disengagement can therefore be identified qualitatively according to the variation of the energy amplitude of the HHT spectrum. (3) The HHT spectrum curves of the vertical acceleration of the carriage and bogie fluctuate significantly. Thus, the starting point of local disengagement can be determined by considering the speed of the train and the local minimum point of frequency curve in the HHT spectrum.

Key words: shield tunnel, traintrack vibration, monolithic track bed, disengagement identification, HilbertHuang transform