Statnamic Load Testing (STN)
Historically load testing of piles has been limited to static and dynamic tests. More recently Rapid Load Testing (RLT) techniques like Statnamic (STN) and Statrapid (STR) have been introduced, which have benefits over the existing techniques.
The most commonly deployed form of Rapid Load Testing is referred to as ‘Statnamic™’, which has been in regular use throughout the world since the early 1990s. The technique was originally conceived in the late 1980s through a collaboration between Berminghammer Foundation Equipment and TNO Building Research. It was developed to incorporate the advantages that dynamic pile testing has over static pile testing without the disadvantages. With an ever increasing emphasis in inner cities to reuse foundations (especially piles) techniques to examine the performance of piles without the need for large reaction systems are of great interest.
The Statnamic test applies a force to the pile head over a typical duration of 120 milliseconds through the controlled venting of high pressure gas. The gas is the product of the combustion of a fast burning fuel within a piston (fuel chamber). At the top of the piston are vents that are sealed by a load hanger retaining a reaction mass. At some point the pressure within the piston is high enough to force the reaction mass upward at accelerations in the order of 500 m/s2. This process generates a downward load on the test pile, resulting in pile velocities up to 1 m/s.
For foundation design it is necessary to derive the ‘equivalent’ static load-settlement curve from the Statnamic data. The most common method to do this is referred to as the Unloading Point Method (UPM).
The proper application of the Unloading Point Method (UPM) is prescribed in the Cur 230 Dutch Guideline for the interpretation of Rapid Load Testing results.