Shape effects in the dynamical response of flints/boulders during pile driving

In the last decade, offshore wind industry has grown exponentially, especially in Europe where is installed more than 80% of the total power of the active offshore wind turbines. In order to bring cost of wind power to a competitive level, dimension and capacity of the new wind turbines are increasing over the year, leading the foundations designers to new engineering challenges. In the offshore environment about 20% of the total cost of a wind turbine is represented by the foundation, which today is largely constituted by large diameter piles often larger than 6m. The need to reduce the foundation cost and increase the pile diameter led to the installation of piles with an increasing diameter to pile wall thickness over the year. This expose in some case the pile toe to be damaged during the installation phase, due the impact with a boulder, widely encountered in glacial tills, or flint bands frequently found in chalk deposits, causing premature refusal. This problem is becoming more and more a concern in the offshore industry and represents a very complex engineering challenge, due to the interaction of several elements. Essentially, the problem can be divided in two main phenomena: •??The pile tip buckling; •??The dynamical behavior of embedded flint/boulder. This thesis is part of a wider research project, where the whole phenomena is numerically investigated. In particular, in this thesis the following of a numerical study of the static and dynamic reaction offered by a flint to the pile tip is presented. The work is mainly aimed to the exploration of the effect of the shape of the flint/boulder, taking into account the possibility of a non-centered impact between the pile toe and the encountered nodule element.