CFA

CFA with helical pile technology

The CFA or continuous helix pile is a dry-drilled pile, therefore without the burden of managing bentonite slurry to support the borehole walls. The technology is based on the rotation of a continuous helix with an excavation tool placed at the lower top and configured according to the soil to be excavated.

The propeller, welded to a hollow tube through which the concrete passes during the casting phase, is coupled with a mast that, in addition to performing mechanical functions and allowing the vertical translation of the head, allows to control the verticality of the hole.

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Processing steps in CFA technology

The executive procedure is very simple as well as the configuration of the equipment on site: the drilling machine provides the excavation by combining the twisting of the propeller with the pull-down; once reached the height of the bottom of the excavation, the concrete is cast, usually by a tracked pump that receives the mixture from a truck mixer.

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The ascent is controlled by the operator who makes use of the on-board instrumentation which, in addition to allowing monitoring, records significant data for possible report printing. An inverted arm excavator gives service to the work by moving and accompanying the casting pipe and removing the result from the mouth.

Once the casting is completed, the reinforcement is lowered into the fresh concrete by its own weight. The manageable diameters range from 400 to 1200 mm. The smaller the diameter, the greater the deviation of the trajectory of the propeller during excavation and the depths are related to the stratigraphy of the site; on average, pole lengths of up to twenty meters can be managed.

Greater lengths can be achieved with the aid of an extension at the head of the propeller called a "shaft" that works by passing through a mandrel: this expedient is not always accepted since the first few meters of excavation, those affected by the shaft, remain uncovered, i.e. there is no lateral protection of the hole with the danger not only of failure of the walls, but also of contamination of the concrete during the casting phase.

These piles are frequently used for their cost-effectiveness, organizational simplicity and speed of execution; unfortunately, they do not offer any guarantees regarding the verticality/linearity of the excavation path and may be subject to shear in the presence of groundwater.