CMC rigid inclusions and ground improvement considerations under wind turbine foundations

Foundation systems for wind turbines are subject to large cyclic bending moments throughout their lifetime. In unfavourable ground conditions, the turbine foundation under these loads may not meet stability and serviceability requirements unless a form of foundation support is used including deep piling, stone columns, rigid inclusions, or other alternative measures which improve bearing capacity and reduce long term settlements. This paper describes the factors to be considered when choosing a foundation support option and presents a case study on the Controlled Modulus Column (CMC) rigid inclusion design supporting most of the turbine pad foundations at the Granville Harbour Wind Farm. The design of the CMC system was analysed using numerical methods which predicted that the bearing capacity, expected settlements and dynamic rotational stiffness would meet the turbine foundation design requirements.