In cases where the ground is not strong enough to be stable while a hole is drilled, the sides of the hole must be supported during the drilling, caging, and concreting stages.

There are a number of techniques for supporting the sides of bored holes for pile construction including:

• Kelly Casing
• Vibro casing
• Oscillator casing,
• Bentonite support
• Polymer support

Kelly Casing is useful for stabilizing bored holes between 600 and 1.5m diameter, up to 50m deep and does not rely on vibration to penetrate. The specially designed and built casings are fitted with teeth and screwed into the soil with additional sections being added as necessary.

The Kelly system bores out the soil from within the casing, reducing friction and allowing additional length of casing to be penetrated into the soils.

The piling rigs must be fitted with specific design casing drivers and the rotary must have sufficient power to drive the casing, therefore smaller piling rigs do not suit this technique.

The casings can be used multiple times with ongoing maintenance and refurbishment required.

The process is quiet and produces piles with little risk due to the design enabling each hole to have casings extended or shorted as the geology dictates.