Testing Pile Foundations at the ΕΤΗ Zurich Drum Centrifuge: Recent Developments

Motivated by the need to develop rational design methods for the retrofit of existing bridges on pile groups, the paper introduces recent experimental developments at the ETHZ Drum centrifuge. Four setups are developed for vertical, pushover, combined, and vibration testing. Their capabilities and limitations are demonstrated using as example a 2x1 pile group on dense saturated sand. Single piles are subjected to vertical loading, exploring the role of installation effects and interface roughness. Pushover loading is employed to measure the moment capacity (Mult) of a lightly- and a heavily-loaded group. In contrast to intuitive expectations, the heavily-loaded system mobilises larger Mult. The developed combined loading apparatus is proof-tested for a shallow foundation. Combined loading under constant vertical load is conducted to derive failure envelopes, revealing significant coupling between lateral and moment loading, and confirming the expansion of the failure envelope with increasing static vertical load. The vibration testing setup is proof-tested, confirming the possibility to identify the natural frequency of the system and the small-strain stiffness of the foundation through non-destructive testing. Although the study is fuelled by our ongoing work on pile groups, the developed experimental setups are of general applicability for the study of deep and shallow foundation systems.