WINDMILL FOUNDATIONS ON WEAK SOILS

Abstract: Much scientific evidence indicates that the Earth's climate is changing and the world has become more concerned about the global climate. This has encouraged many countries to consider future clean power production with wind power taking an increasing part. In Sweden, the government declared the intention of generating 30 TWh/year from the wind by 2020 instead of 7.1 TWh/year achieved in 2012. Egypt, a developing country with a population of more than 90 million, has also specified that the Egyptian wind power share will reach 20% by 2020 instead of 1% in 2014. To achieve these goals, hundreds of new wind turbines will definitely have to be built, requiring prompt and extensive studies on how this can be achieved.On weak soil, supporting structures constitute the larger share of the cost of modern wind turbines after the turbine itself. Therefore, the cost can be decreased considerably with an improvement in the design methods of the supporting structures. The objective of this work is to conduct a comprehensive analysis of the geotechnical behaviour and the cost of three new foundation solutions and to examine their performance in comparison to the conventional foundation solutions. To achieve this objective, settlement and tilting response of the new and the classical foundations are investigated by using finite element analysis together with a cost comparison between the new and the traditional foundations.The new foundation solutions designed are a conical raft, a flat circular raft surrounded by a water tank, and a conical raft surrounded by a water tank to decrease the foundation cost and to improve the geotechnical behaviour of the foundation. A comparative study of the mentioned foundation solutions has been performed numerically using finite element simulations. The results of the current study show that the geotechnical behaviour of a conical raft is improved compared to the geotechnical behaviour of a flat circular raft if the same diameter is used. Also, the conical raft requires less concrete and rebar volume to pass requirements on settlement and tilting. Concerning the active foundation solution using water tanks, the idea is to use a movable load to balance the overturning moment in order to decrease the tilting. It is shown that there is an economic benefit of this active system compared to the use of piling. The results show that using the active foundation solution can reduce the foundation tilting compared to a piled raft with long friction piles on deep soft clay layer. Also, the initial cost of the water tank foundation is less than the initial cost of the piled raft.