Special seismic phase in wave field induced by high-speed train and its applications

Studying the characteristics of seismic wave field excited by high-speed trains can help us to invert underground structures by using high-speed rail sources, serving high-speed rail safety monitoring, smart city construction, etc. The high-speed rail seismic wave field with evenly distributed bridge piers as the source has obvious interference characteristics. The specific spacing of the bridge piers determines that the main frequency, pier frequency, corresponding to the time interval between a train passing the two bridge piers and the frequencies near the double pier frequency can interfere and increase. However, during the construction of high-speed rail viaduct, due to the consideration of vibration and noise reduction factors, the recorded main frequency generated by the train itself cannot be superimposed and enhanced, making the energy of the high-speed rail seismic signal lower. In the analysis of actual observation records, we find some special phases in the high-speed rail seismic wave field. For trains traveling in different directions, this seismic phase occurs before or after the train's arrival time, and is related to the train's running speed. Therefore, this article speculates that this seismic phase is related to the special pier spacing, and the change in the distance between some piers, which causes the dominant frequency to appear. Through the calculation of the simulated wave field, we obtain a high-speed rail seismic waveform much similar to the actual record. Using these energies with large amplitude and high signal-to-noise ratio, it is possible to obtain the velocity structure and its change over time along and near the high-speed rail.