Rationalising Specifications for Bentonite Slurries and Polymer Excavation Support Fluids

Bentonite slurries have a long history of successful use for the construction of bored piles and diaphragm walls and in other operations such as slurry tunnelling and horizontal directional drilling. In parallel, polymer fluids based on high molecular weight partially hydrolysed polyacrylamides are now well established as support fluids for the construction of bored piles. All support fluids must be properly managed at all stages of the cycle of use from preparation of fresh fluid, through completion of the constructed element to recovery of the fluid for reuse. Fluid management practice will vary between countries as the local base products themselves vary and also as construction and regulatory practices differ. Furthermore excavations may pass through a variety of soil types. It follows that specifications for bentonite slurries and polymer fluids can be expected to vary between countries, users and soil types reflecting the behaviour of products available, user practice and plant. It would be naive to think that for either bentonite slurries or polymer fluids, a single specification can be suitable for all locations, soil types and works procedures and also across all bentonite and polymers. This paper considers key properties of support fluids and how these can be reflected in specifications for their operational control.