Bored Pile Starter Guide

A bored pile is a non-displacement form of foundation that is cast in situ and provides economical load bearing solutions suited to a wide range of ground conditions and applications. The drilling method depends on the soil condition so a soil investigation is required prior to determination of a method of piling. A method should be chosen based on minimising disturbance of the surrounding soil and its effectiveness in drilling through the ground conditions.

Construction Methodology

  • Complete an access track for the piling rig/excavator with the required area to operate in.
  • A trial bored hole should be undertaken to confirm soil investigation results and to check for the groundwater level.
  • The survey should set out off-set pegs at 90-degree angles to the centre of the pile.
  • The auger should be moved into position and checked from the off-set pegs prior to the commencement of drilling.
  • The depth of the pile should be measured and marked onto the auger using tape or similar.
  • Slowly start auguring, making sure the auger is in a vertical position at all times. A spotter may assist with this.
  • The auger will pull out of the hole in order to disperse the material to the stockpile.
  • Checks should be made from the offset pegs to show that the auger is in the correct position. This should be repeated until the required depth is achieved.
  • A visual check of the condition of the augured hole should be undertaken to ensure that the hole has not collapsed and is free of tree roots and debris.
  • The pre-fabricated re-enforcement cage should be checked prior to lifting into the augured hole for compliance with the specification.
  • Once lifted into position and cast-in items have been hung, the survey should set cast-in bolts for the line and level.
  • Check for cover before pouring the concrete.
  • Before the commencement of each concrete pour, sufficient vibrators and spares should be available.
  • The concrete should be poured using a chute and deposited as near as possible.
  • The concrete should not be allowed to fall freely for more than 2m unless using suitable chutes or baffles are used

Design

  • Consideration must be given to the ground conditions and the water table levels.
  • Concrete mix design must take the site conditions into account.
  • Consideration must be given to the design of the reinforcing cage in relation to bolt configuration and the vibration requirements during installation.

Advantages

  • For many design situations, bored piles offer higher capacities with potentially better economics than driven piles.
  • The absence of vibration.
  • Soil removed in boring can be inspected and if necessary sampled and tested.
  • Multiple holes can be augered prior to the placement of concrete.
  • Only minor earthworks are required to auger.
  • The length can be readily changed to suit varying ground conditions.

Limitations

  • Sensitivity to operator performance.
  • Dewatering is required if water is encountered.
  • Unfavourable geotechnical ground conditions can result in augured holes collapsing.
  • Poor ground conditions can cause slow productions.

Quality Tips

  • The design team, construction team and piling contractor should meet to agree on methodology prior to the work commencing.
  • A test pile should be installed and tested prior to main works commencing to fully evaluate ground conditions.
  • Groundwater boreholes should be checked prior to commencement.
  • An experienced piling operator is vital to ensure piles are bored correctly and steel reinforcement has the specified cover.
  • The number of piles that can be concreted in a day should be taken into consideration to ensure the concrete is placed to specification.
  • Sacrificial encasement should be used in poor ground conditions to minimise the risk of the ground collapsing.
  • Survey control is vital for the pre-pour and post-pour checks to ensure the bored piles are within specification for line and level.