Restrike-XL

XL monopiles are very attractive and economical foundations for offshore wind power plants. From installation point of view, the vibratory driving method appears to be advantageous because 1) XL monopiles can be better handled by vibratory driving, 2) the pile is prevented from being impaired by the installation, and 3) the harmful sound emission for sea mammals is significantly reduced. In the case of vibratory driven pile, it is assumed that the designed pile-bearing capacity cannot be achieved, therefore, additional hammering is required (EAP, 2012).

The current design methods for deep foundations have been developed for hammer driven piles. It is unclear how the set-up effect, which occurs after pile installation and positively affects the pile-bearing capacity over the service life, differs in hammer and vibratory driven piles. In order to close this knowledge gap, in 2014 in the "VIBRO-PROJEKT", pile tests were carried out on vibratory and hammer driven piles in the Monopile test field in Altenwalde. After approximately 3 years of service life in 2017, dynamic pile loadings were conducted on the same piles again and accompanied with additional measurements through the "Set-Up XL-Monopile Restrike Monitoring" project. This unique data base forms the basis for this project and allows for the first time to compare and quantify the long-term set-up of hammer and vibratory driven piles of offshore XL monopiles. With the help of further laboratory and field tests as well as numerical modeling, the causes and effects of the set-up effect are investigated. This enables us to calibrate and evaluate the pile design methods as well as new modeling approaches for numerical analysis with consideration of the pile set-up effect. A better understanding of set-up effect and utilizing technologies to quantify it have high economic and ecological advantages. The requested project is based on the specific characteristics of the site in the EEZ of the German North Sea.

The aim of Restrike-XL is to investigate the phenomenon of long-term increase of pile capacity for both hammer and vibratory driven offshore XL monopiles based on pile loading tests from the industrial projects VIBRO-PROJEKT and VIBRO RE STRIKE. The causes and effects of this increase in pile capacity are the main focus.