Echo in the mountain: Sonar technology for application in tunnel excavation

Dr. Rüdiger Giese from the GeoForschungsZentrum Potsdam (GFZ) and his team receive the “Technology Transfer Award 2008” from the Technology Foundation Brandenburg for the development of a new system for use in tunnel pre-exploration, the ISIS.

The ISIS (Integrated Seismic Imaging System ISIS) is a method which enables the preliminary exploration of the rock mass in a tunnel. The technical innovation here in lies particularly in the fact that with this procedure sounding-explosions are no longer necessary and the system can be employed while actual tunnel construction work is running. Herewith tunnel excavation will be safer, faster and more efficient.

In spite of all progress to date, tunnel construction is still a technical and economical risky undertaking. The biggest imponderability is that an exact pre-exploration of the rock mass in which the tunnel drilling machine has to drill is essential. To investigate the rock material in front of the tunnel drilling machine seismic procedures are usually applied: a small explosive charge is ignited and the propagation of the explosion’s sonic waves are evaluated. For this purpose the tunnel drilling machine has to stop operation and construction work is interrupted. – with costs of around 100 Mio. Euro for such a machine, a significant cost factor.

And this is where the ISIS comes to use. The ISIS allows for the forecasting of the geological characteristics of the rock mass in the surroundings of tunnel excavation in advance and without disturbing drilling procedures to any great extent – similar to ultrasound in medicine.

“The idea is to use the tunnel-anchor, to install a measuring system for seismic three-component receivers with their antenna in such a way that a high-resolution seismic image of the rock mass during excavation is possible” says Dr. Rüdiger Giese. “Small earth-microphones (geophones) serve as receivers, which are implanted in the pinnacles of the rock anchor. Herewith the different seismic waves can be supersensitively compiled. The data gives information on changes in the rock mass and eventually on water-bearing stratum”.

The anchors are cemented in meter-deep boreholes. They can be fixed radial to the tunnel or in the direction of tunnelling. The seismic impulses are triggered with a pneumatic hammer or an electromagnetic vibration source, whereby the impulses radiate in the specified direction and can be repeated in intervals of seconds.

And all this can take place during the ongoing tunnelling procedure.

The system has already been applied during the construction of the new St. Gotthard tunnel and in the tunnelling of Nessy’s home, Lough Ness.

“We are pleased that we could obtain Herrenknecht AG, the global market leader in tunnel excavation as our partner for the market launch of the ISIS System. This is thanks to the excellent work of Herr Giese’s team. I heartily congratulate Dr. Giese on receiving this award”, says Professor Dr. Reinhard Hüttl, Scientific Executive Director of the GFZ Potsdam on this occasion.