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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
systems are available which are more tolerant of ionic species in
soils and these should be used in saline grounds.
4 CONCLUSIONS
Through the use of case histories and recent research findings,
this paper has outlined some strengths and limitations of
polymer fluids as potential replacements for bentonite slurries
particularly for small or congested sites. Strengths include
improved foundation performance, simpler site operations and
reduced environmental impact. Limitations include reduction of
fluid properties due to continued shear in recirculation systems,
potential for loss of properties in saline soils and importantly
sorption of polymers onto soils – which also can be a benefit as
it reduces dispersion of fines into the fluid. To minimise the loss
of fluid properties, fresh polymer must be regularly added to the
system otherwise a significant degradation in performance of
the fluid and potentially the foundation element will occur.
5 ACKNOWLEDGEMENTS
Figure 6. Effect of added sodium chloride on the viscosity of a
commercial blended polymer product and a pure PHPA both mixed in
deionised water.
3.4
Loss of active polymer concentration due to repeated use
The properties of polymer fluids depend on physical and
chemical interactions between the polymer molecules in
solution. An excavation polymer is thus an active chemical
system. Whilst in use in an excavation, polymers tend to sorb
onto soil surfaces, especially those of clays and this can
beneficially reduce the break-up of lumps of cut soil and the
resulting dispersion of fines into the fluid. However, it does
follow that the concentration of active polymer drops with use
and unless the concentration is regularly re-established the fluid
will become little more than muddy water, a condition which
the authors have dubbed as ‘flipped’. The system has ceased to
be polymer solution with some suspended soil and become a
soil slurry with little polymer remaining in solution.
The work presented in this paper was undertaken as part of a
research project jointly funded by the UK Engineering and
Physical Sciences Research Council (EPSRC), Balfour Beatty
Ground Engineering and KB International LLC. EPSRC grant
reference nos.: EP/C537815/1 (Industrial CASE award) and
EP/H50026X/1 (Knowledge Transfer Secondment). The authors
would like to thank Messrs T. Suckling, V. Troughton,
C. Martin, P. Martin and G. Goodhue for their help and advice
throughout the project.
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Figure 7. Reduction of polymer concentration by sorption.
