Double Rotary System (Cased CFA)
Cased CFA piles is a state-of-the-art method for pile installation. It requires the use of heavy-duty large piling rigs with high torque capacities. The method requires the use of two rotary heads driving a heavy duty hollow-stem CFA auger in a clockwise direction into the top soil, while at the same time rotating a casing in counter-clockwise direction such that the toe of the auger and the bottom of the casing are at about the same level during the advancement of the drilling process.
Upon reaching the design pile depth and in a manner identical to CFA piles, the concrete is pumped through the CFA auger, but this time it is constrained by the full length casing. This helps maintain a perfectly circular pile shaft with a very tight control on verticality.
Double Rotary Secant Pile Walls
Secant pile walls are formed by interlocking reinforced concrete rotary bored piles. Double rotary secant pile walls are constructed with the Double Rotary Method (Cased CFA) by using drilling rigs such as our Liebherr LRB 255 and LRB 355. Alternate primary piles, comprising of unreinforced concrete, are installed first; then secondary, reinforced concrete piles are installed in between the primary piles, once the latter gain sufficient strength. The pile overlap is typically of the order of 100mm to 150mm depending on the depth of excavation and degree of ‘watertightness’ required.
