Vibratory Installation Study of a Monopile in Dense Sand

Abstract

The assessment of monopile installation by means vibratory driving is discussed for a platform located in the Dutch Sector of the North Sea. The vibratory driving analysis of the 4.7 m diameter monopile was performed using the “Hypervib” method in order to evaluate the performance of a 960 kg.m excentric moment vibrohammer. The results of the installation study indicated that the monopile could be installed up to a penetration depth of 31.5 m considering the full nominal power and frequency (23 Hz) of the specified vibrohammer. The frequency of the vibrator is shown to influence the projected penetration of the monopile. In particular, the “Hypervib” method indicated that refusal could be encountered if the effective frequency of the vibrator dropped below 20 Hz. As a consequence, monitoring measures were recommended to mitigate/characterize the risks of early refusal.