Double rotary drilling
Double rotary drilling (CCFA)
1. Positioning at the drilling point
2. Auger drilling with simultaneous advance of the casing
3. Extraction of auger and casing while concrete is pumped in through hollow stern
4. Inserting the reinforcement
5. Finished pile
Double rotary drilling combines continuous flight auger drilling with a continuous casing. Casing and auger (inside the casing) are simultaneously installed and extracted. Double rotary drilling is applied for the production of cast-in-place piles and for predrilling.
Examples with double rotary drilling
Combination of continuous flight auger and casing
This method combines continuous flight auger drilling with a casing. It is mainly applied for producing cast-in-place piles.
Double rotary drilling
Two rotary drives are separately mounted on the sledge and independently drive the inner continuous flight auger and the casing.
Installing cast-in-place piles
During the drilling process the auger flights convey the drill cuttings to the surface inside the casing. Through an opening at the upper end of the auger the drill cuttings are ejected.
“Front-of-wall” drilling
The compact design of the double rotary head allows operation very close to existing building structures, i.e. in front of building walls.
Protection cover
A protection cover encloses the casing so creating an annular space inside. Thus, the ejected drill cuttings fall to the ground in a controlled manner.
Emptying the auger
After their extraction, casing and auger are swung to the side and emptied by rotating the auger in the reverse direction.
Extracting and concreting
After the final depth has been reached concrete is pumped through the auger’s hollow stem. During the extraction process the concrete exits at the lower end of casing and auger.
Reinforcement
After concreting a reinforcement cage can be inserted in the column of fresh concrete. For this purpose the auxiliary winch of the carrier machine is used.
