Sonar Technology for Tunnel Drilling
For
developing a new system for use in tunnel pre-exploration Dr. Rüdiger Giese
from the GeoForschungsZentrum Potsdam (GFZ) and his team have received the
Technology Transfer Award 2008 from the Technology Foundation Brandenburg.
The ISIS (Integrated Seismic Imaging System ISIS) is a method that enables the preliminary exploration of the rock mass in a tunnel. The technical innovation here is that with this procedure, sounding explosions no longer are necessary, and the system can be employed while actual tunnel construction is taking place.
In spite of all the progress to date, tunnel construction still is a risky undertaking. The biggest challenge 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 ahead of the tunnel drill, seismic procedures usually are applied: A small explosive charge is ignited, and the propagation of the explosion’s sonic waves are evaluated. Under these circumstances, the tunnel drill has to stop operation, and construction work is interrupted – at a significant cost.
Here is where the ISIS comes into 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 super-sensitively compiled. The data gives information on changes in the rock mass, and eventually on water-bearing stratum.”
The anchors are cemented in 3-feet-deep boreholes. They can be fixed radial to the tunnel, or in the direction of tunneling. 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 tunneling procedure.
The system already has been applied during the construction of the new St. Gotthard tunnel and in the tunneling of Lough Ness.
The ISIS (Integrated Seismic Imaging System ISIS) is a method that enables the preliminary exploration of the rock mass in a tunnel. The technical innovation here is that with this procedure, sounding explosions no longer are necessary, and the system can be employed while actual tunnel construction is taking place.
In spite of all the progress to date, tunnel construction still is a risky undertaking. The biggest challenge 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 ahead of the tunnel drill, seismic procedures usually are applied: A small explosive charge is ignited, and the propagation of the explosion’s sonic waves are evaluated. Under these circumstances, the tunnel drill has to stop operation, and construction work is interrupted – at a significant cost.
Here is where the ISIS comes into 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 super-sensitively compiled. The data gives information on changes in the rock mass, and eventually on water-bearing stratum.”
The anchors are cemented in 3-feet-deep boreholes. They can be fixed radial to the tunnel, or in the direction of tunneling. 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 tunneling procedure.
The system already has been applied during the construction of the new St. Gotthard tunnel and in the tunneling of Lough Ness.
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