A novel experimental technique to model impression piles in centrifuge testing

Abstract

A novel experimental technology for small scale centrifuge tests on piled foundations has been investigated. The technology is suitable for bored piles where the pile shaft has been profiled to improve the bearing capacity. One such pile is an impression pile that has an enhanced shaft capacity due to the small impressions created along the shaft. In previous centrifuge testing, impression piles have been created by pouring resin into a profiled bore. However, in the technique to be described a novel pile made of 3D printed rigid plastic with a reverse mandrel mechanism is used to create a nodular shaft surface during installation in the clay sample. Once assembled the pile has the same geometry as the cast in situ impression pile. Compared to the resin piles, 3D printed plastic piles allow for faster model making and demonstrate excellent repeatability. Because of the ductile behaviour of the soil-plastic interface it is possible to see how the impressions improve the performance of a pile over the whole load-settlement curve, not just at ultimate capacity. In addition, a greater percentage increase in ultimate capacity was registered for the 3D printed plastic impression piles compared to similar resin impression piles. The plastic-soil interface has an α value which is closer to that commonly encountered in the field. At working load, the 3D printed plastic impression piles outperformed traditional straight shafted piles by 90%.