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Crosshole and downhole seismics: a new quality assurance tool for jet grout columnsNormal access

Authors: J.C. Galindo Guerreros, E. Niederleithinger, S. Mackens and T. Fechner
Issue: Vol 14, No 6, December 2016 pp. 493 - 501
DOI: 10.3997/1873-0604.2016042
Language: English
Info: Article, PDF ( 1.3Mb )

Abstract:
Sealing and strengthening of the subsoil by grout injection is a major issue in the field of geotechnical engineering. One commonly applied method is jet grouting, which allows creating columns of grouted soil by eroding and mixing the in-situ soil with a thin cement suspension. A general difficulty linked with this method is in predicting the resulting column diameter and its material strength. In this paper, we illustrate the application of a newly developed non-destructive quality assurance tool used to determine the diameter of jet grout columns. This approach incorporates standard crosshole and downhole seismic measurements. To demonstrate its effectiveness, we tested the new approach within two-dimensional finite-difference numerical simulations. Additional field tests showed that this tool is also applicable in real site conditions. For this purpose, three jet grout columns were produced with different process parameters in a depth between 3 and 10 m. The evaluated diameters were within 1 and 1.5 m, slightly deviating from the previously predicted range by the jet grouting contractor. Moreover, we were able to detect the base of the columns at a 10-m depth with no significant difficulties. On the other hand, unsaturated, less compacted sands between the groundwater level and surface considerably affected the seismic data, hence complicating the detection of the top of the columns.


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