The use of polymer solutions for deep excavations: lessons from Far Eastern experience

Abstract

Solutions of water-soluble polymers have been used to stabilise deep excavations such as pile bores and diaphragm wall trenches since the 1970s. When compared with conventional bentonite slurries, these engineered fluids are recognised as bringing a number of benefits including smaller site footprint, lower environmental impact and lower construction costs. However, despite the years of use, too little has been published about their material properties and optimal methods of use, so problems still occur. To promote the best practice with these engineered fluids, this paper summarises the lessons that may be drawn from a number of published case histories of polymer use in the Far East. It is concluded from the review that the use of biodegradable polymers in deep excavations can be problematic unless a biocide is used. In contrast, synthetic polymers tend not to suffer from microbial degradation but do require the use of special pumping equipment to minimise shear degradation. In coarse soils, both types of polymer fluid can show excessive fluid loss. This can be remedied by adding bentonite, superabsorbent gel particles or proprietary fines that are dispersible in polymer fluids. Finally, soft pile bases have been reported which can be linked to the use of low fluid viscosity coupled with long waiting times between the end of excavation and concreting. This can be minimised by rigorous fluid and base cleaning. Overall, the case histories show that polymer fluids cannot be managed as if they were simply bentonite slurries. Their usage require different procedures, which, in turn, require different skills and experience from a contractor. This paper concludes with an analysis of future challenges and opportunities with these innovative construction fluids.

Keywords:

• bored piles
• barrettes
• deep excavations
• polymer solutions
• support fluids

Funding

The case histories discussed in this paper were studied as part of three research projects funded by the UK Engineering and Physical Sciences Research Council (EPSRC) [Grants EP/C537815/1 (Industrial CASE Award), EP/H50026X/1 (Knowledge Transfer Secondment) and EP/K503782/1 (Impact Acceleration Account)].

Additional information

Ir Dr Carlos Lam graduated from The Hong Kong Polytechnic University, Imperial College London and the University of Oxford in 2001, 2003 and 2011, respectively. He is a Chartered Civil Engineer and a Registered Ground Engineering Specialist in the UK. He has been conducting research on the use of polymer fluids for geotechnical construction since 2007 and has published extensively on this topic. Prof Stephan A. Jefferis and Ir Dr Lam are the authors of a technical book entitled “Polymer Support Fluids in Civil Engineering”, which will be published by ICE Publishing in 2015.

Prof Stephan A. Jefferis is the Director of Environmental Geotechnics Ltd, a Visiting Professor at the University of Oxford, an Emeritus Professor of the University of Surrey and currently the Vice Chairman of the British Geotechnical Association. He has over 40 years of experience in research and consultancy on geotechnical processes. He has worked extensively and internationally on the application of bentonite, bentonite-cement and polymer slurries in piling, diaphragm walling, tunnelling and cut-off walls. He is the author of over 100 papers and is regularly invited as a keynote speaker.