Support Fluids for Piling in Urban Areas: Preparation, Operation and Specification

Developments on urban sites often require the installation of deep, large diameter piles (drilled shafts).  Typically these will require the use of an excavation support fluid. Synthetic polymer solutions have become the fluid of choice for constrained urban sites because, when appropriately managed, they offer the following benefits:  Elimination of soil-slurry separation plant – these are items of plant with significant site footprint, substantial operating and maintenance costs, demands on personnel and potential for noise nuisance; Avoidance of the disposal of heavy used slurry during the works; Reduced water usage – the fluid can be systematically reused, with additional polymer being added to the fluid after each use; Drier spoil – the excavated soil can be drier and so easier to transport and reuse, and,  Easier support fluid disposal – at the end of the works, the polymer fluid can be broken to meet the local sewage undertaker’s requirements for discharge to sewer or in some jurisdictions, for environmentally compliant polymers, direct discharge to the environment.    The paper will compare and contrast the use of synthetic polymer fluids and bentonite slurries and identify situations which favour / disfavour the use of one fluid system over the other – no one system can meet all conditions.