HOSTED BY Effects of polymer and bentonite support fluids on the performance of bored piles Carlos Lam a,n , Stephan A. Jefferis b , Tony P. Suckling c , Viv M. Troughton d a Geotechnical Engineering Office, Civil Engineering and Development Department, The Government of the Hong Kong Special Administrative Region, Hong Kong, Formerly School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, United Kingdom b Environmental Geotechnics Ltd., and Department of Engineering Science, University of Oxford, United Kingdom c A-squared Studio Engineers Ltd., Formerly Balfour Beatty Ground Engineering Ltd., United Kingdom d Arup Geotechnics, Formerly Balfour Beatty Ground Engineering Ltd., United Kingdom Received 29 November 2014; received in revised form 1 July 2015; accepted 21 August 2015 Available online 27 November 2015 Abstract Synthetic polymer fluids have been used for the construction of bored piles (drilled shafts) for more than two decades, but their effect on the performance of the completed piles is still a matter of debate. To investigate the effects of polymer and bentonite fluids on the behaviour of bored piles, a field trial comprising three full-scale instrumented test piles has been conducted at a site in East London. It was found that the two piles constructed using polymer fluids showed much stiffer load-settlement response than the one constructed using bentonite slurry. Surprisingly, an extended pile bore open time of up to 26 h was found to have no adverse effect on the piles if supported by polymer fluids. Based on the results of back-analyses using the load-transfer approach, polymer fluids were found to have little effect on the Woolwich and Reading Formations but a noticeable effect on the Upnor Formation – the mixed results are believed be due to the different soil mineralogies. It has also been shown that the common problem of ‘soft toes’ can be eliminated by adopting good construction practice including proper base checking and fluid cleaning or exchange procedures on site. & 2015 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved. Keywords: Synthetic polymer; Bentonite; Support fluid; Excavation; Bored piles 1. Introduction For the construction of bored piles and diaphragm walls, fluids are often used to support the excavation side walls in unstable strata until concreting. Bentonite clay slurries have been used for this purpose since the pioneering work by Veder (1953). Synthetic polymer fluids have also been used success- fully on many projects since their introduction to the founda- tion industry in the early 1990s. The polymer fluids considered in this paper are aqueous solutions of high-molecular-weight polymers, having essentially the same density as water but a much higher viscosity. Compared to bentonite, polymer fluids can offer many operational and environmental benefits includ- ing: smaller site footprint, ease of mixing, lower fluid disposal cost and less impact on the environment (e.g. Schünmann, 2004; Lennon et al., 2006). A general introduction to polymer fluids can be found in Jefferis et al. (2011) and Jefferis and Lam (2013). Because polymer fluids are both physically and chemically different from their bentonite counterparts, there is still a lot of debate about how these fluids compare in terms of their effects The Japanese Geotechnical Society www.sciencedirect.com journal homepage: www.elsevier.com/locate/sandf Soils and Foundations http://dx.doi.org/10.1016/j.sandf.2015.10.013 0038-0806/& 2015 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved. n Corresponding author. Peer review under responsibility of The Japanese Geotechnical Society. Soils and Foundations 2015;55(6):1487–1500