Rock Mechanics and Rock Engineering

, Volume 40, Issue 1, pp 81–95 | Cite as

Additives for Slurry Shields in Highly Permeable Ground

  • P. Fritz


For tunneling projects in saturated soils tunnel boring machines (TBMs) with slurry shields are widely used. However, in coarse, highly permeable soils the suspension penetrates the ground and the required support pressure cannot be built up. For the Zimmerberg Base Tunnel near Zurich permeabilities much greater than 10−3 m/s were expected. This value is usually considered as the critical limit for the applicability of slurry shields. Therefore it was aimed to find additives for the bentonite suspension which would allow it to attain a higher suspension pressure.

For these investigations an apparatus has been developed. It allows the maximum attainable support pressure for a given suspension and a ground to be determined. It reflects the real situation, produces reproducible results and is insensitive to the inevitable variation of individual parameters.

In the tests the additives polymer, sand and vermiculite were studied and their effects on the attainable maximum suspension pressure investigated. For the best combination, i.e. with a well defined proportion of the individual components, suspension pressures could be attained which were about 10 to 20 times higher than those with an ordinary bentonite suspension. Successful excavation of the Zimmerberg Base Tunnel proved the validity of the laboratory tests containing 200 kg bentonite per m3 water.

Keywords: Bentonite, gravel, shield, slurry, soil, suspension, TBM, tunnel. 


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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • P. Fritz
    • 1
  1. 1.Institute for Geotechnical Engineering IGT, Swiss Federal Institute of Technology ETH-ZZürichSwitzerland

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