Design of offshore caisson foundations for wind turbine structures

Caissons are special foundation types used to support structures in challenging ground conditions and in offshore environments. Pneumatic caissons have been used for bridge foundations, for example the Brooklyn Bridge in the USA. Open caissons and box caissons are particularly common in Japan, India and other parts of Asia, at locations of river crossings and marine structures.

Geotechnical design of caissons starts from preliminary selection of caisson type, material, dimensions, and installation method, based on key parameters such as load resistance requirements, soil profile, groundwater conditions, and environmental constraints. This requires consideration of factors such as construction feasibility, economic viability, durability, and sustainability.

This paper provides a detailed overview of the conceptual design principles
for caisson foundations, drawing from project case studies and best practice guidelines and design codes used in various countries. It is found that, in comparing North American, European and Asian practices: (a) design philosophies and methods used in the USA are grounded mainly on safety factors, robust documentation, and innovative construction technologies , (b) in European regions, design practice is heavily reliant on quality assurance and design can be based on deterministic and probabilistic approaches, with use
of various partial safety factors as stipulated in the Eurocodes, (c) In Japanese practice, seismic design requirements are fundamental considerations and in India there is significant emphasis on pneumatic sinking and mass concreting methods due to variable field conditions, especially for onshore sites.