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.
- 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
- 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.
- 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.
- 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.
- 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.