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

Abstract

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 also 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 and so 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.

Ageing behaviour of polyacrylamide-based excavation fluids

“…The operating principle of the Brookfield viscometer is the measurement of the shear stress acting on a rotating cylinder (spindle) immersed in the test fluid. The same viscometer was used by Lam et al (2014c) to study polymer sorption onto soils. The standard spindle LV-1 was used for all the ageing tests.…”

Interpretation of Viscometer Test Results for Polymer Support Fluids

“…However, since the early 1990s, synthetic polymer fluids have been used successfully in many projects around the world (e.g. Lam et al 2010;Jefferis and Lam 2013;Lam et al 2014). The flow behavior of polymer fluids is very different from that of their bentonite counterpart and yet no distinction is currently made between the two types of fluid in terms of the interpretation of viscometer results.…”

Construction techniques for bored piling in sand using polymer fluids

“…For example, the viscosity of the fluid can be significantly reduced by the use of unsuitable pumping equipment and by contaminants in the ground (Jefferis and Lam, 2013;Lam et al, 2010b). Uncontrolled reuse of the fluid can lead to depletion of the active polymers (Lam et al, 2014b). Previous experience has also shown that the use of these fluids can increase the risk of 'soft toe' and concrete contamination due to the settling of suspended soil particles (Brown, 2004;Fleming et al, 2009).…”