CFA piles

Technology of construction and production of reinforced concrete piles with CFA technology

Reinforced concrete piles with Continuous Flight Auger (CFA) technology:

The CFA method is used for unstable terrain, it is very effective for loose and unconsolidated materials. The execution technology itself is efficient and fast, because all operations take place continuously, without interruption.

The application of CFA technology requires the involvement of special machinery such as MAIT HR 180. The machines have special tools with "endless drill".


The method of performing CFA piles has three operations:

  • Drilling

  • Concreting from the bottom up, via an endless drill, which is attached to a self-pump through which concrete is injected through the machine system.

  • Reinforcement

  • Lowering the arm basket to the projected depth (elevation).

Given the specific weight of mechanization, as well as the manufacturing technology itself, the work platform must be adequately prepared:
  • Well-planned wild material and rolled.

  • On a substrate prepared in this way, make a gravel curtain with good compaction from 30 MPa to 35 MPa.

  • The prepared terrain should enable drainage from atmospheric precipitation, as well as extraction from the well itself, if any.

  • The working plateau should be ready at least 3 m within a radius of the pile axis due to the correct movement of the machine.


The terrain prepared in this way enables the movement and proper operation of the engaged machinery and equipment, proper centering, leveling and better work performance.

It is necessary to adjust the working plateau so that the mechanization can move backwards and perform the previously mentioned operations.

It is recommended to bring the working plateau at the level of the top of the anchor, in order to lower the reinforcement baskets to the concrete mass, and also to leave the part prescribed for tightening the pile head. Also, the working plateau prepared in this way enables the movement of machinery, without distorting the armature anchors.

Before the start of work, the machine system itself is connected to the auto-pump. After connecting the system, it is necessary to pump cemet milk through the auto-pump systems and the machine system. Cement milk is made from 3 bags of cement and water.

The self-pump must have all the information about the dimensions of the concrete injection piston as well as the remote adjustment of concrete pumping speeds, it is definitely recommended that the self-pump has its own concrete flow measurement system All data on the car pump should be provided for compliance. It is not recommended to change car pumps due to constant data correction and adjustment of concrete flow.

CFA pile technology:

  • Before the start of drilling, it is necessary to mark the exact position and center of the spike with a steel anchor 30 cm long.

  • The mechanization is brought to the exact position of the pile, the tower is leveled and the drill is lowered to zero, which adjusts the computer in the depth-determining machine. It starts with drilling. During the drilling itself, it is necessary for a smaller excavator or JCB to clean the ground around the drill with a profile spoon, which is taken out of the pit itself through an endless drill. Diagrams and well depths are monitored via a computer in the machine cabin itself.

Concreting technology:

Before concreting, a sample is taken from the auto-mixer and poured using an Abrams cone. The required pouring of concrete should be from 56cm to 60cm.

  • When the pile is drilled to the bottom of the projected pile level, concreting begins through the system itself and the endless drill of the machine. Concrete is injected into the machine system with an auto-pump. It is concreted from the bottom of the pile upwards, where the diagram of the movement of the concrete itself and the pouring of the concrete mass in the pile pit itself is monitored via a computer in the machine. It is concreted to the top of the elevation of the working plateau. The concreting of the pile itself must be continuous and uninterrupted, which requires continuity in the arrival of concrete mass on the construction site. Minor delays during concreting can be tolerated, while the auto-mixer changes to the left-hand drive of the auto-pump.

    During the concreting of the pile, the flow of concrete and the appearance of the pile in the hole itself is monitored with the help of a computer from the machine, so that the driver always has an insight into the appearance of the pile and concrete consumption. With the help of a computer, the consumption of concrete itself can be reduced. At the end of the works, data are taken from the computer and a detailed report on the pile is obtained.

  • The mechanization is brought to the exact position of the pile, the tower is leveled and the drill is lowered to zero, which adjusts the computer in the depth-determining machine. It starts with drilling. During the drilling itself, it is necessary for a smaller excavator or JCB to clean the ground around the drill with a profile spoon, which is taken out of the pit itself through an endless drill. Diagrams and well depths are monitored via a computer in the machine cabin itself.

Reinforcement technology:

Before the end of concreting, the reinforcement basket must be ready and assembled completely, due to the length of the reinforcement basket, it must be welded one hundred percent and fixed, so that the basket does not bend or fall apart during lifting.
It is certainly allowed to reinforce the pile up to 2/3 due to the very moments it receives, the reinforcement basket in this case accepts the forces of pressure and transfer to the concrete that can meet the projected load.

  • After the concreting is finished, the earth is removed from the pile pit and a reinforcing basket is inserted into the fresh concrete mass. The reinforcement basket is raised vertically, with the help of a machine, centered above the pile pit and lowered into the fresh concrete mass.

  • During the reinforcement itself, if the basket is not lowered to the projected elevation of the pile depth, a hydraulic converter (vibrating cap) is placed on top of the basket and with the help of vibrations produced by the converter, the reinforcement basket is lowered to the projected elevation.

    Of course, before installing the vibro cap, the excavator can press it in by pressing the armature basket lightly. If the reinforcement basket remains protruding from the ground, it is necessary to cut it to the ground level due to further movement of equipment and machinery.

    The elevation of the top of the pile or the elevation of the top of the reinforcement must be equal to the working plateau, due to the movement of heavy machinery so as not to trample the baskets and bend the reinforcement.

    When the armature basket is installed, the drilling machinery can be easily positioned in the next position of the pile and drilling can be started. During reinforcement, the installation itself must not be delayed, any minor delay may cause the reinforcement not to fall to the projected elevation.

When drilling CFA piles, since it belongs to DRILLED piles, there is no effect on the bearing capacity of the pile if the pit is broken again. The advantage of CFA piles compared to conventionally drilled piles is that when injecting concrete through the machine system, concrete is compacted into the pile sheath and thus increases its load-bearing capacity, while with conventionally drilled piles the load-bearing capacity of the pile is not as high. which only fits evenly with the wrapper.

Depending on the characteristics of the terrain, it is sometimes necessary to drill the pile to a certain level in order to make it easier later for concreting, which must be done without interference and difficult work.

Execution of secant piles

Method of execution of "CFA" secant piles is:

  • Drilling to the required level and concreting unreinforced piles from the bottom to the top, via an endless drill bit, which is attached to a car pump, through which concrete is injected through the machine system
  • After one day (until the concrete has not yet fully set and reached greater strength) from the execution of non-reinforced piles, the approach is made reinforced piles , ie drilling and concreting from the bottom up, through an endless drill, which is attached to an auto-pump through which concrete is injected through the system. This is followed by the reinforcement of the mentioned piles (inserting the reinforcing basket into the fresh concrete mass)

The folding of the reinforced and non-reinforced pile is 5.0 cm on both sides. The grade of reinforced pile concrete should be less than the grade of reinforced pile concrete. For reinforced concrete piles (mostly) take MB30 , while for non-reinforced piles take MB20 or MB25 . It is enough for the unreinforced piles to be 1.0 m deeper than the excavation level.

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