Physical modelling of pore pressure development during impact pile driving using geo centrifuge

Abstract

During the last decade, the focus of offshore activities have shifted from oil and gas production to offshore wind farm creation to reach the clean energy targets set by different nations. Foundation requirements for offshore structures have shifted because of this. The monolithic nature of windmills allows the use of a single open-ended steel pile as a foundation. While their installation procedure is similar to onshore piles, the dimensions of these open-ended piles are of a different scale, measuring up to 8 meters in diameter and 80 meters in length. The hydro mechanical response of the soil and the soil-structure interaction during the installation of the piles is complex and not yet fully understood. To better comprehend the soil behaviour during installation Royal IHC has initiated a research project in collaboration with the TU Delft. The current study is part of this research project. Using advanced physical and numerical modelling methods, a first step is made to gain better insight in the soil behaviour.

Using advanced physical centrifuge modelling techniques this study aims to provide insight into the soil behaviour and pile response during impact pile driving. The model can help validate numerical models and provide a controlled test environment for further modelling. To achieve this a new model impact pile driving setup was developed. This setup is capable of modelling the blow rate and impact energy of offshore pile driving hammers. A new data measurement system and sensor equipment was also created to capture parameters such as pore fluid pressure, blow rate, impact speed and pile displacement. Model piles can be installed in a controlled and repeatable environment. Special care has been taken to achieve correct coupling between the hydro mechanical response and the impact driving in the model.

Preliminary results from the model show no major scaling or modelling errors compared to numerical results. However validation of the model is needed and could be done by using a case study. The setup itself is operating efficiently and is highly adaptable for future research goals. The tests performed during this research were limited due to time constraints. Installation parameters such as pile displacement and pore fluid pressure development are in the range as expected. Furthermore, a correlation was seen between the radial distance from the pile tip and the increase of pore fluid pressure. Comparison of pile displacement with numerical models show similar results. Future studies should focus on varying impact pile driving parameters such as blow rate, blow energy and impact speed to define a correlation between the development of pore fluid pressure and impact pile driving parameters. This could improve the future efficiency of impact pile driving. The long term effects on the stability of the foundation should be regarded in future studies.