Dynamic Formula for Pressure Injected Footings

The mathematical derivation of a dynamic pile-driving formula for the installation of Pressure Injected Footings (Franki Piles) is presented. The usefulness of such a formula, despite the inherent limitations of all dynamic formulas, is demonstrated. The necessity of differentiating between the two fundamental methods used to make the shaft of a Pressure Injected Footing is proposed and load-test data then presented which support the proposition. An example of how to use the formula is given. The formula contains a constant which is a function of the type of soil and type of shaft. If the result of a load-test is available, the constant can be evaluated from the test data. For those cases where no load-test result is available, a table is presented giving suggested values of the constant for various types of soil and shaft.