Guidance for the reader

Breasting and mooring dolphins are installed in inland waterways, adjacent to jetties and waiting facilities, for ship-to-ship transhipment or as crash barriers in commercial port areas. These marine structures were originally constructed on the basis of trial and error and mainly consisted of wooden piles. Around 1900 it was possible to perform fairly simple calculations in order to estimate the strength and deformation characteristics of dolphins. In 1930, Dr Hermann Blum developed a more advanced method for the design of horizontally loaded piles. This method has been used ever since, although alternative design models are available, such as p-y curves and finite element methods. The use of steel as a construction material was also introduced around 1930. However, up until the 1950s, wood remained the main construction material in the design of dolphins. In the Netherlands, flexible dolphins realized since the 1950s are predominantly laterally loaded steel tubular piles with large pile diameters and high ductility in order to achieve economy of design.

The line loads of moored ships cause static lateral loads at the top of a dolphin's pile head. Dolphin piles are defined as flexible dolphins because of the contribution of the pile deflection to the absorption of berthing energy. Breasting dolphins are often installed with a fender system or a wooden timber structure to reduce hull pressure during the landing procedure of a vessel, as well as to protect dolphins and the structure directly behind them, which can be a jetty, bridge, lock or storm-surge barrier. The different types of dolphins are described and discussed in chapter 2.

Although a dolphin's structure is rather simple, its design is relatively complex since the structure needs to provide both support (minimum deflection) and energy absorption (through flexibility). The latter results in the uncommon condition that high soil strength becomes unfavourable, which is not common for geotechnical structures. At present, the diameters of thin-walled steel tubular piles are increasing, as are their D/t ratios. This has a positive effect on the mobilized passive soil wedge, but a negative effect on ductility, the capacity of cross sections and drivability. A sudden collapse due to local buckling before large deformations develop should be avoided because no warnings are received before failure. The most important design aspects are discussed in chapter 3, which presents the state of the art of the available knowledge with regard to essential design aspects and methods presently available in the industry. In the Netherlands, flexible dolphins are classified as geotechnical structures and they have to comply with the Eurocodes. Unfortunately, clear guidelines for dolphins have not been implemented in the Eurocodes and detailed design guidance is lacking. This often results in a fairly conservative design compared to existing flexible dolphins. Although code compliance is important, existing dolphins are performing quite well and the asset portfolio of flexible dolphins in the Netherlands is in good condition, which does not logically support the need for more conservative designs. Hence, chapter 4 presents four case studies that were used to compare the available design models and safety philosophies and techniques for dolphins. The theoretical background to existing design methods was based on a limited amount of prototype testing. To increase reliability and safety, more insight was obtained by performing a full-scale field test in the Port of Rotterdam (see appendix A1) that investigated in detail not only geotechnical failure but also the effects of local buckling and excessive yielding. To derive reliable conclusions concerning the actual performance and failure modes, test piles were loaded until a structural failure or an impending collapse occurred. The more advance design aspects – such as piles in slopes, drained and undrained soil behaviour, and repetitive loading – are discussed in detail in chapter 5. The main objective of this guideline is to provide engineers, asset managers, suppliers, tender teams, contractors and principals with guidance on the design and construction of flexible dolphins. The results and insights reported in chapters 1–5 were used to develop a design approach for flexible dolphins. The steps in the design approach are described in chapter 6, and the construction is covered in chapter 7. This latter chapter provides quite useful information for the designer with regard to procurement, fabrication, material properties, drivability and decommissioning. Another important aspect is the equipment installed on flexible dolphins – such as fender systems, the platform, bollards, quick release hooks and lighting/illumination – which is described in chapter 8. The lifecycle aspects and sustainability in the design of a flexible dolphin are highlighted in chapter 9. Finally, the lessons learned are presented in chapter 10.

This guideline is intended to obviate extensive discussions during the design and construction stages of projects involving flexible dolphins. It is part of a series of Dutch port infrastructure design recommendations, such as the Quay Walls handbook, the Jetties and Wharfs handbook, and the Banks handbook.