At a job-site in Austria it was needed for building a railway tunnel to install a deep excavation support. The given soil were gravel and sandy gravels with high permeability in connection with groundwater level near by the surface, the river Inn is near by the job-site. For dewatering the excavation the pumping volume for the groundwater was limited. So it was needed to install a bottom plug, as shown in the following section, to cut off water from the bottom of excavation.
Installing the bottom plug the contractor used the Jet-Grouting system, the single columns were placed in overlapping Triple- Geometry. In the following Excavation support it was needed to cut off the groundwater using a Bottom Plug in a depth about 20 m, 60 ft, as shown:
The following picture shows the result from the Test at the job-site in Columbus/OH (presented in the Paper GeoDenver 2007) in the known kind of Analysis the catch waves, sourced by the Jet, using FFT. Shown is the overlapping between two neighboured columns, one column during installing (working Jet), the other column done. You see exactly the overlapping from 3 jets (blue mountains).
Result from Test Austria Excavation Support (Steel-Sheet in connection with Bottom Plug, Depth about 20 m (60 ft):
In FFT- Analyzing you see very clear the Form/Geometry of Steel sheet while 1 Jet is overlapping the Steel Sheet Piling. Additional amazing was in this test using the system for catching the waves. The most important however result was, that contrary to overlapping of two neighboured columns, where you don’t know the exact surface of both columns, here you know about the exact surface of the steel sheet and you can compare the result of wave analyze with the geometry of this special surface of a steel sheet, the jet hit. Other results about the fact how the jet worked could be won, in first priority the connection between the treated soil around the steel sheet, in connection with the installing process of steel sheet piling, and the fact or possibility using air for a jet support (Jet-Grouting-double-system).
Together with University of Munich a better visualization was figured out, however, it’s still not the end of the development.
The target is the fact that for the Owner it is better to show not to much complex data, as in FFT-Analyzing (3D) shown above. It may be better to show a clear result, means Overlapping given or not given, and for given situation “overlap”, how great is the overlapping angle right now during the installing process, and to compare it with the planned situation.
Also for installing at the job-site and for the personal here a clear result, like “job done” or not, is the most important result for the Quality-Control-System.
Here for is still some work to do, this depends in a deep sense also from transferring the data from and while (in realtime) the installing process is running.
So it is needed or more better to finish the development in a close work together with the Special foundation Contractor. Perhaps in a next step an optimizing the Jet-Grouting process for saving costs while QC may be possible.