First OK for New Lightweight Gravity Foundation

The Maritime Offshore Group GmbH (MOG) from Bremen (Germany) performed successful the first stability calculations together with the Technical University of Central Hessen, “Civil Engineering and Architecture” (Professor Dr. Christine Doebert) for a gravity base offshore foundation in a new lightweight design.

Although the combination of characteristics may not make any sense, the new foundation is a serious planned new product of the MOG. The “TEXBASE” called structure has been designed under the same strategy as the first structure of the MOG, the HEXABASE. A lightweight design using spiral- and longitudinally welded steel pipes will be ballasted by six concentrically arranged sand ballast tanks with a maximum volume of about 3,000 tons of sand.

The particular characteristic of those tanks are the material used: They will be made of a special robust fabric that is permeable to water, but not for sand. The ballast tanks are arranged above the feet of the structure and will be pumped up with a mixture of sand and seawater. The water will be separated from the sand and the ballast will solidified.

The total empty weight of a typical TEXBASE designed for a usual 6 MW wind turbine will be about 750 tons. The whole structure will be placed on six steel tube frames covered by the same fabric as the ballast tanks. The foundation could be lowered to the seafloor with just very minor preparation of the ground.

With the need for the pile ramming the most important problem for foundation installation is eliminated – the extreme underwater noise generated by the hammer and often an important problem for the authorities and the environmental protection boards. The installation planning for the TEXBASE will only depend on the weather conditions.

The TEXBASE is planned for the economical series production as the HEXABASE before. Many identical components and different production lines will benefit from the volume effect known from the automotive industry.

Any steel parts of the structure will be coated by a new developed multilayer coating on based on polyurethane plastic. After the final assembly the structure will be cold sprayed on the primer pre-treated surfaces with a layer having a thickness of 2 to 3 millimetres. The new TEXBASE will be calculated and designed in any details for the next months. A certification of a reputed classification society will be the next step.