The On-Site Management of Polymer Support Fluids for the Construction of Drilled Shafts and Diaphragm Walls

This paper sets out the site procedures to be adopted when using polymer fluids as alternatives to bentonite slurries for excavation support. These fluids are now accepted as alternatives to bentonite slurries for the excavation of drilled shafts and diaphragm walls. Field trials have shown that they can give better shaft friction and lower concrete overbreak than traditional bentonite slurries and yet they have fluid properties that utterly contradict the norms established for bentonite slurries. For example, the rheology of polymer fluids is quite distinct from that of bentonite slurries–they have effectively no gel strength and the appropriate operating range of Marsh funnel times for a polymer fluid may be from 60 to over 100 seconds, markedly higher than for bentonite slurries and yet clean displacement of the excavation fluid by concrete is achieved. In contrast, specific gravities are markedly lower with that for fresh polymer fluid at 1.0, that is, the SG of water and typically a maximum prior to concreting of <1.02. It will be shown that site-operating practice with polymer fluids is also very different from that with bentonite slurries. For example, no soil-fluid separation plant is required (that is, no screens, hydrocyclones, centrifuges etc.). Also fluid disposal is necessary only at the end of a job and after minor treatment can be to municipal sewer.