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Franki Driven Cast-in-Situ Piles

The Franki pile has been used extensively throughout Southern Africa for the past 60 years and is still today one of the most popular pile types. With a wide range of pile sizes and the advantages of the enlarged base, the Franki pile is suited to structures that vary from single-storey residential buildings to multi-storey office blocks. There are also some interesting variations in the installation technique which have special applications.

Positive Features

  • The Franki pile is often a very economical system
  • There is an extensive range of pile sizes
  • The Franki pile has an excellent load / deflection performance
  • Noise levels are relatively low
  • The Franki pile has excellent tension load capacity

Other Considerations

  • Vibration associated with the driving of the piling tube and the formation of the enlarged base
  • Pile heave in saturated cohesive soil profiles

The main feature of the Franki pile is the enlarged base formed at the toe of the pile. In forming the enlarged base the end-bearing area is increased considerably. Furthermore, the displacement achieved when expelling the plug and forming the enlarged base compacts and pre-loads the soils surrounding the base. Thus the end-bearing of a Franki pile in sands develops at much lower base deflections than that of a bored pile.

   
 

 Optional Special Techniques

1.            Expendable driving rings and / or bentonite lubricating skin to aid penetration and extraction in cohesive soils.
2.            Jetting, pre-drilling and / or coring through the tube to improve penetration and /or to reduce vibration.
3.            ‘Conditioning’ of very soft ground before forming shaft.
4.            ‘Sliding ring’ to increase shaft diameter in softer upper layers.
5.            Additional depth with extension tubes of up to 6m.
6.            Top driving of tube with expendable end plate.
   

 
FRANKI PILE INSTALLATION SEQUENCE

   
 

A. A plug of sand / stone is placed in the piling tube and compacted with a hammer. B. The tube is driven by applying blows of the drop hammer to the plug which arches in the tube and draws the tube into the ground. C. On reaching the founding level the tube is held by the extracting gear while the plus is expelled using blows of the hammer. D. Measured quantities of relatively dry concrete are expelled from the toe of the tube thus forming an enlarged base. E. The reinforcing cage is placed in the tube which is then filled with high slump concrete. F. The tube is extracted by means of the extraction gear. On deeper piles the concrete level may have to be topped up during extraction. G. The completed pile.

   
 
 
 



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