Continuous Flight Augering, sometimes known as auger cast piling, is a technique to create concrete deep foundations.
A continuous flight auger drill is the same length as the required hole depth, and concrete is injected through a hollow shaft under pressure as the auger is extracted. Reinforcement is inserted after the auger is removed, creating a continuous pile without ever leaving an open hole.
Fifteen years ago, CLL was introduced to CFA piling when visiting a contractor in Sydney. Soon after, we visited rig manufacturers in Italy, and our first CFA rig was soon on the water heading for Auckland.
The CFA technique is significantly quicker than other piling methods.
One of the most significant advantages of CFA is the fact that there is no raising, cleaning and lower of tooling into the hole as it is being drilled, which anyone who has experienced it knows, generates a very high level of disruptive noise.
By installing the concrete from within the base of the auger as it is removed negates any need to support the sides of the bored hole which saves time and money.
CFA requires rigs with plenty of power and will not be used on ground which is consistently stronger than 5mpa because of the strain this would place on the long drill string.
CFA is not suitable where piles need to be dead drilled to end at a basement level yet to be excavated.
“As you take the soil and spoil out, you’re filing the hole with concrete from the bottom up. It means the hole never depressurizes and is never unsupported, it is always engaged and you have no problem with groundwater. It is especially good on poor soils. CFA minimizes the amount of gear and machinery you have to have onsite, though you do have to have a rig that can generate a fair bit of torque.”
“It is also a technique that lends itself to repetition. In a 500 pile project for example, CFA might allow us to put in 20 a day. Other standard methodologies, using casing for example, you’ll be lucky to do four a day. CFA can significantly lower the price of piling. It’s a method our Tauranga branch in particular employs when dealing with the collapsing sands stratas they have there.”
— Juan Santacruz