This system is commonly used for heavily loaded structures where the soil profile is saturated over all or part of the profile resulting in unstable side-wall conditions for conventional auger piles.  The term ‘underslurry’ indicates that the pile is excavated under a head of bentonite slurry, which prevents collapse of the pile excavation.  Both auger and grab excavation methods can be used, resulting in circular and rectangular cross-sections.  These two methods are referred to as Auger Underslurry and Barettes, respectively.

Positive Features

  • Economical pile solution for heavy structures on saturated soil profiles
  • Noise levels are low and limited to engine noise from the equipment
  • There is no vibration associated with underslurry piles
  • A good range of pile sizes from 600mm to 1500mm diameter
  • Underslurry piles can be installed to depths in excess of 50 metres
  • Barette type piles can be shaped

Other Considerations

  • High establishment costs
  • Large site area required
  • Suited to heavily loaded structures only
  • Only vertical piles can be constructed
  • The slurry-contaminated spoil must be disposed of at an approved waste site

The maximum depth to which Barettes can be installed is really unlimited, but a practical limit of 60 metres is suggested.  Barettes cannot be installed on a rake.