Tunnel Seismic While Drilling - An Efficient Tool For Geological Prediction Ahead Of The Tunnel Face

Abstract

Summary The Tunnel Seismic While Drilling (TSWD) method has been developed and applied at several tunnel sites to predict the geological situation ahead of the tunnel face during mechanical tunnel driving. When tunneling with a Tunnel Boring Machine, the vibrations of the drilling head, resulting from the cutting process, offer to be employed as a seismic source signal, ensuring a continuous seismic monitoring without hindering the drilling and driving operations. With the appropriate signal processing the continuous monitoring data can be converted to conventional seismic traces from which relevant fault zones within a geophysical forecast window of up to 100 m ahead of the current tunnel face can be predicted. Since the implemented instrumentation, data transfer and logistics guarantee processing on a daily basis, significant geological structures can be observed over long distances. The TSWD-method gives excellent continuous seismic data, from which deeply incised valleys, karst cavities, fault zones and other unexpected degradations of rock quality can be predicted. Wider fault zones over a thickness of 10 m can be successfully resolved, smaller fault zones are largely detected, depending on seismic impedance contrast and the position relating to the tunnel axis.