Double Rotary CFA
From the time we started with CFA it has always been the dream of the CLL team to get a double rotary rig because of the superior accuracy and speed that they enable.
About 7 years after introducing CFA, CLL bought a DRCFA rig from Perth.
The technique is particularly valuable when constructing secant walls and the piles produced form a very accurate clean line.
Unlike conventional top-drive rotary rigs, a double rotary has two counter rotating rotary drives working simultaneously but in opposite directions.
The hydraulic top-drive rotates the drill string. The lower independent rotary drive advances a steel casing through unconsolidated overburden. This casing’s rotation provides borehole stability.
CLL currently owns and operates 5 double rotary CFA rigs.
Double rotary CFA has all the advantages associated with CFA but adds superior accuracy and also complete elimination of the risk of flighting or decompressing the ground during drilling.