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. © 2010 ASCE