How to ensure clean pile base when using bentonite or polymer fluid?

[Kiri Robbie]

For end bearing type of pile, how can we ensure to clean the pile base properly if we use bentonite or polymer fluid? There could be a formation of thin layer of of 20-30mm settlement soil particles between interface of concrete and rock.

[Martin Larisch]

Very good question. We could use weighted tape measures to assess the 'hardness' of the base. This is still a common method to estimate the thickness of the debris layer at the base prior to concrete placement (not cage installation).

Typically the tremie process could be used, to 'flush' the base as the concrete flows down the tremie pipe and displaces the fluid from inside tremie pipe. The fluid that is pushed out of the tremie will flush a thin layer (about 50mm thick) of debris off the base. If the layer is thicker, concrete placement should not commence. However, this criterion is project specific.

It is important to use the correct cleaning tools and to ensure that flat cleaning buckets are used which fit the pile diameter. don't attempt to clean a 900mm diameter bored pile with a 600mm cleaning bucket...

Pumps or air lifting could also be used to clean the pile base.