Determination of Residual Concentration of Active Polymer in a Polymeric Support Fluid

This paper is concerned with the properties of synthetic polymer fluids used for the temporary support of excavations, such as pile bores and diaphragm wall panels. These fluids can be used as alternatives to bentonite slurries and may influence the performance of the foundation elements formed under them. During the excavation process, polymers tend to be sorbed onto the soil and they may be degraded by the shearing in pumps, etc. It follows that a controlling parameter for these fluids is the residual concentration of active polymer in the fluid, and this paper considers test methods that may be used for its determination. Three different measuring principles, namely, total organic carbon, UV light absorption, and viscosity, were investigated for their suitability for site use. Their performance was compared in a series of polymer-clay sorption experiments-the clay sorbing the polymer, therefore reducing the residual concentration in solution. A method based on the measurement of viscosity of centrifuge supernates was found to have the best overall performance. A comparison with current assessment criteria based on Marsh funnel viscosity and density measurements confirmed the superiority of the proposed method for detecting polymer loss by sorption. Further evaluations showed that the proposed method is not limited to any specific combinations of polymers and soils. The proposed method will allow site engineers to have greater control over the properties of the fluids on site.