Stephan A. Jefferis

Observations on viscosity reduction of PHPA polymer support fluids

Polymer fluids have been used in foundation drilling for many years and yet no previous studies have been reported which assess their sensitivity to shear such as is induced by pumping equipment. A field study has been carried out on two specific polymer products under actual site conditions. It is found that there is a significant loss of viscosity when partially hydrolyzed polyacrylamide (PHPA) fluids are circulated through a centrifugal pump in a loop system. This behavior is quite distinct from that of bentonite slurries which require high shear mixing and recirculation to ensure good hydration. At first sight the sensitivity of PHPA fluids to shear may be perceived as a disadvantage but in fact if shear can be reduced so can on-site energy consumption. A reduction in fluid viscosity was also observed over a standing period between mixing and use, suggesting that a second mechanism may be contributing to the properties change. From the trial results, recommendations are given on pump selection and on the maintenance of fluid properties.

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

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.

Physical Properties of Polymer Support Fluids in Use and Their Measurement Techniques

This paper was concerned with the physical properties of polymeric excavation-support fluids during use and reuse in the field and the techniques for their measurement. Synthetic polymer fluids were used as replacements for conventional bentonite clay slurries for the construction of bored piles (drilled shafts) and diaphragm walls since the early 1990s. They are used, in part, because of their rheological properties, especially their shear-thinning behavior, but to date research has focused on clean fluids and little also has been reported on the effects of reuse under field conditions and on the suitability of viscosity measurement devices. To fill this knowledge gap, the properties of polymer fluids were measured on a construction site in London, UK, over the entire construction period of 52 days. It was found that the density of the fluid and hence other properties were highly dependent on the decisions made by the contractor and that a well-designed tank system could offer considerable benefits in terms of fluid maintenance. Regarding the monitoring of fluid viscosity, the Marsh funnel was, unsurprisingly, found to be unsuitable for detailed analyses; although it did provide some useful information about the overall fluid condition. However, with a direct-indicating viscometer, it was possible to characterize the shear-thinning properties of the fluids over a range of shear rates and stages of fluid use. From the test results, it was concluded that the effect of reuse was to increase in the overall fluid viscosity but at the same time to enhance the shear-thinning behavior.

Interpretation of Viscometer Test Results for Polymer Support Fluids

Polymer support fluids have been successfully used for the construction of bored piles (drilled shafts) and diaphragm walls for many years and yet there is currently little guidance on the interpretation of their rheological properties from viscometer test results. In particular, there is confusion about the choice of an appropriate rheological model for this type of fluid. The use of oilfield units by some has also added to the confusion. To promote the use of SI units, this paper summarizes conversion factors that can be used to present viscometer data in a more uniform manner. Simple rheological concepts and instrument-specific equations are also given for those unfamiliar with the issues. Viscometer test results for two polymers fluids are then used to illustrate the application of the power-law model over the shear-rate range achievable with a typical direct-indicating viscometer.

Performance of Bored Piles Constructed Using Polymer Fluids: Lessons from European Experience

AbstractSolutions of synthetic water-soluble polymers have been used for the construction of bored piles (drilled shafts) since the early 1990s. These engineered fluids are very different from conventional bentonite slurries but there is currently a serious lack of industry guidance. Despite their advantages over bentonite, performance issues have arisen in the past and foundation engineers remain wary of their use. To help practicing engineers avoid past pitfalls and to promote best practice, this paper presents a critical reappraisal of selected European case histories of bored piles constructed using polymer fluids. A collective reassessment is necessary in order to provide an overall picture of the situation as individual cases may show conflicting results. It is found that the completed piles can have excellent load–movement characteristics if polymer behavior is understood and respected. Conversely, excavation instability, structural defects, and poor pile performance can result if the special prope...

Reply to the discussion by Fellenius on 'Critical assessment of pile modulus determination methods'

First of all we would like to thank the discusser for his interest in our paper, which deals with the determination of pile modulus for the interpretation of loading test results. As can be seen in the reference section of our paper, the discusser has made significant contributions to the study of this topic over a substantial period of time and we are therefore delighted to address the issues he has highlighted and to elaborate some key points.

Erratum for “Performance of Bored Piles Constructed Using Polymer Fluids: Lessons from European Experience” by Carlos Lam and Stephan A. Jefferis

Please note the following correction to the final published paper. The viscosity value in the fourth sentence of the second paragraph of the Introduction should be 10 mPa · s, not 10 MPa · s. The sentence should therefore read, “Unlike bentonite, polymer fluids do not form a gel when left undisturbed (nonthixotropic) and have negligible yield stress, although they can still have very high viscosity, up to 10 mPa · s at low shear rates (Lam et al. 2015).” The error was inadvertently introduced during typesetting. ASCE regrets the error.

Corrigendum: Critical assessment of pile modulus determination methods

Received 16 March 2012. Accepted 16 March 2012. Published at www.nrcresearchpress.com/cgj on 30 April 2012. C. Lam. Department of Engineering Science, University of Oxford, Parks Road, Oxford, Oxfordshire, OX1 3PJ, UK. S.A. Jefferis. Environmental Geotechnics Ltd., St Mary’s Grove, 4 Adderbury Park, Adderbury, Banbury, OX12 3EN, UK; Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX1 3PJ, UK. Corresponding author: Carlos Lam (e-mail: carlos.lam@eng.ox.ac.uk and carloslam@hotmail.co.uk). 630