Untersuchung der Pfropfenbildung an offenen Verdrängungspfählen

Investigation of the Plugging Effect of open ended piles

The plugging effect of open-ended piles and hence the change in the load bearing behavior has been investigated in this research work. The state of knowledge assumed that the plug can close up the pile base completely and for this reason it was treated monolithically. The load bearing behavior was comparable to a closed-ended pile. But the soil-mechanical processes were mostly unknown.
The experimental part contains model tests and PIV-(Particle Image Velocimetry) tests. The test piles were arranged with equipment for measuring each part of the pile resistance (inner and outer shaft resistance and resistance of the pile toe). Because of variation the boundary conditions the main influence factors of the plugging effect could be analysed.
Furthermore numerical calculations with the FEM were carried out, which show a good agreement between the experimental data and the calculations. The investigations show, that the load transfer in the plug occurs in an inner shaft friction. A fully plugged soil could not be identified and so the classical model representation could be disproved.
Based on this results an analytical calculation method is derived, in which each proportion of the pile resistance could be determined. Finally in the statistical part new values of experience for the pile resistance are suggested for the EA-Pfähle.