Method of building a foundation comprising a steel monopile and a concrete part and associated foundation for construction work

A method of building a foundation comprising a steel monopile and a precast concrete part on top of the monopile, the method comprising:

• arranging a support structure inside the monopile, the support structure having a plurality of rods extending radially with respect to a longitudinal axis of the monopile;
• driving the monopile into a ground (G);
• bringing the precast concrete part above the monopile, with supporting columns interposed between the support structure and a transverse abutment surface of the precast concrete part to transfer the weight of the precast concrete part to the monopile,
• wherein reinforcement bars protruding from a bottom surface of the precast concrete part extend downwardly beyond the support structure by passing between the rods of the support structure;
• arranging tendons between the support structure and the precast concrete part and tensioning the tendons to pre-stress the supporting columns;
• and
• pouring concrete into an upper part of the monopile such that the support structure and the supporting columns are embedded in concrete.