Installation und Tragverhalten von Bucketgründungen für Offshorebauwerke

Installation and bearing behaviour of bucket foundations for offshore structures

A bucket foundation consists of one or, in case of a jacket or tripod structure, of three or four steel cylinders with a steel lid on top, which is installed offshore by pumping water and thus inducing underpressure below the lid. This installation method, which is the reason for the often used term 'suction bucket', is rather simple and avoids driving noise emissions. This makes it an interesting alternative to usual offshore foundations with driven piles instead of buckets. However, the installation process must be accurately calculated and controlled to avoid hydraulic failure, buckling and inadmissible rotations. Moreover, open questions regarding the bearing behavior of bucket foundations particularly under transient or cyclic loads exist. The paper firstly presents methods for the prediction of penetration resistances during installation and applies them exemplarily for typical soil conditions of the German North Sea. Secondly, the specific requirements on the behavior of buckets for offshore wind energy converter foundations are described and the respective state of knowledge is outlined. Finally, the basics of a general design concept for buckets as foundation elements of offshore wind energy converters are presented and open questions are discussed.