Prediction of geological anomalies ahead of tunnel face by seismic waves

Abstract

Geological anomalies such as weak zones, water-filled cavities may cause problems during tunnel excavations, for instance, the loss of stability at tunnel’s face, flooding, reduction in excavation rate, etc. Thus, the knowledge of geological anomalies in advance is beneficial for safety and operation planning. The potential to predict geological anomalies ahead of tunnel face by seismic waves called Tunnel Seismic Prediction is investigated in this study. The study is performed on artificial seismic records generated by Spectral Element Method on a numerical model which includes a geological anomaly. The synthesized waves are processed by F-K filtering to extract only waves in relevant velocity range and directions before processed by Kirchhoff’s migration with a consideration on the vibration axes. Results from the migration are images showing locations where the reflections of waves occur, or in other words, the location of geological anomalies. The results show that the irrelevant waves can be excluded by the proposed technique resulting in a better prediction for the location of assumed anomaly in the synthesis model.