Franki Piles, also known as enlarged based driven cast in-situ piles, are cast-in-place elements constructed using a drop weight (hammer) and temporary casing. They can provide high capacity piles with relatively shallow installation depths.
A 400mm to 550mm diameter temporary steel casing is vertically positioned at a planned location.
The bottom few meters of the casing is filled with a dry concrete mix and a drop hammer is used to compact the dry concrete. The dry mix then locks into the bottom of the casing forming a driving plug. This driving plug is then impacted with the drop hammer to drive the temporary casing into the ground until design depth or founding layer is reached. Once the founding toe level has been reached the casing is secured from advancing using restraining cables. The plug is then expelled from the temporary casing by dropping the impact hammer.
Once the plug has been expelled, additional dry concrete mix is added in specific controlled volumes and expelled from the bottom of the temporary casing to form the enlarged base. By keeping the drop heights of the impact hammer consistent and counting the number of blows for a known volume of dry concrete, the installation energy can be calculated, this volume vs installation energy relationship (by way of the Nordlund energy formula) provides quality assurance for pile founding material.
Upon completion of the enlarged base, reinforcing steel and high slump concrete are then placed in the temporary casing and the casing is then extracted leaving the in-situ concrete, reinforcement and enlarged base to form the permanent pile.
Enlarged Based Frankipiles are installed to an ISO9001 accredited Keller quality system and installed in compliance with AS2159-2009. Forming the quality records are pile base installation energy records and basing charts. Pile load testing (PDA and CAPWAP) and integrity testing (PIT) are carried out when required and test reports submitted with the quality documents. Concrete testing records and steel mill certificates also form part of the quality assurance submission documents.