Optimization of Tunnel Seismic operations for fast and continuous investigations ahead of the face
The knowledge of the geological ground conditions and its geotechnical parameters is still the major problem for driving of a tunnel. Although, underground construction works are increasingly carried out under difficult soil and rock conditions. Significant geological boundaries that cut the tunnel axis can cause serious problems such as large break-outs, collapses, flooding and rush-ins during tunnel advance, especially when intersecting very suddenly or with sub-horizontal striking of the tunnel vault under a sharp angle. This leads to high risks for man and machine.A careful risk management more and more addresses such geological hazards by adequate exploration during tunneling. Tunnel seismics is a robust and reliable prediction method especially when applied in 3-D. However, some tunnel builders still object against geophysical investigations during tunneling due to possible disruptions of the tunneling process and constraints of results delivered by these methods.There is so many case studies published describing the benefits of modern Tunnel Seismic Prediction. In addition to that, developments are continuously going on.Recent optimizations focus on the operation work flow while tunnelling where the seismic wave generation process is being fully integrated. The application of the Multi Shot Recording reduces the data acquisition time to only 10 minutes even when applied in TBM drivage. With this, a prediction range of more than 100 meters ahead of the face is reachable. Furthermore, the same measurement layout enables a focus to the rock mass around the already excavated tunnel performing a dedicated data processing. Thus, essential interfaces from sub-horizontal layering become detectable.Moreover, the Tunnel Seismic Prediction while Excavating technique allows a continuous or permanent prediction ahead or to the side. With this, 3D-images of the P- and S-wave velocity distribution are being constantly updated in intervals of 10 metres according to the requirements prescribed by the complexity of the geological ground conditions.Ground conditions vary throughout the world, and they are one of the major reasons for cost overrun in a project. Research studies give evidence that there is a direct correlation between the amount of site investigations and cost savings. The more investigations have been carried out, the better estimates of project costs match with the real and final projects costs.