Simplified design of new hybrid monopile foundations for offshore wind turbines

摘要

First, a review of knowledge developed over the previous 50 years was presented, including various simplified methods of analyzing hybrid foundations. To discuss this subject comprehensively, a reference to calculations of piles was also made. On this basis, the author focused in the paper on new aspects of designing the hybrid foundations in serviceability limit states. The know-how review showed that the aspects of hybrid foundation design have been poorly recognized so far. For practical reasons, a simple calculation method for the hybrid foundations, useful for initial decision making, is still needed. A new design method was presented, based on a hybrid pile-soil interaction concept. A general design concept was described, the assumptions were formulated, and the method was explained in detail. A practical application of this method has been demonstrated for a large diameter hybrid pile, previously tested at full scale under lateral load. The calculation results were compared with the well-verified data obtained from the field test. By incorporating the extended knowledge on the mechanism of the pile-soil interaction, a significantly reduced horizontal stress in front of the pile was achieved. The conducted calculations confirmed that the hybrid monopile displacement is 40-70% lower compared to the standard monopile with similar dimensions. This method allows the stability of the new hybrid monopiles under lateral load to be assessed in a better way. The gained experiences can be useful for designers and other researchers to enhance the design of offshore wind turbines on monopiles.