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

摘要

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.