The research of τ-p transform applied in the tunnel seismic prediction

摘要

With speeding up of railway construction, the more long and deep tunnels are being scheduled. As the geological condition prediction before the tunnel workface is of significant importance for safety, quality, progress and cost etc. of the tunnel construction, non-destructive geophysical methods, such as high-density electrical survey, electromagnetic methods, seismic reflection method and so on are widely used for the prediction. The seismic reflection method with its longest prediction distance and high resolution among the methods is the most widely used in the geological prediction of tunnel construction. In the seismic prediction, the reflection records are not, however, just the waves being reflected from the ahead of the workface. For the complex geological conditions of the tunnels, many interferential reflections from other directive reflectors are stacked on the ahead reflection records, which may cause some traps for the prediction. As the time-distance curve and apparent velocities of the reflection wave records from the ahead of the tunnel workface with common-source or common-receiver layout are usually of obvious difference from that of the interferential reflections, the τ-p transform with its power function in apparent velocity filtering is of potential to separate the seismic waves of ahead reflectors of the tunnel workface from the other directive reflectors. On the other hand, theτ-p transform usually is important tool for the separation of P-wave and S-wave for the calculation of the ratio of P-wave to S-wave, passion ratio, and other rock physical parameters to evaluate the ahead geology condition of the workface, since the both waves are of the apparent velocity differences. In the paper, we illustrated the superiority and flexibility of theτ-p transform to achieve the reflections from the ahead of the workface, and the P-Wave and S-wave separation under tunnel complex geological condition by numerical model and a real case.