Device for guiding and vertically holding a monopile and method for installing a monopile using such a device

A device for guiding and vertically maintaining a tubular monopile when it is placed in an excavation made in a seabed, filled with compacted granular materials and consolidated by a metal reinforcement tube, comprising:

• a support structure intended to be positioned vertically to the excavation made in the seabed and mounted on at least four feet which are each adjustable in height;
• a frame for positioning the support structure relative to the reinforcement tube, the positioning frame having a closed U shape, being mounted on a low portion of the support structure and being intended to ensure the positioning of the support structure relative to an upper end of the reinforcement tube;
• a cage extending along a longitudinal axis (X-X) and mounted inside the support structure above the positioning frame in order to receive the monopile, the cage comprising a closed low portion and a high portion provided with a door able to open to allow lateral introduction of the monopile into the cage and able to close to maintain the monopile in the cage;
• the high portion of the cage comprises a plurality of damping pads distributed around the longitudinal axis (X-X) of the cage, dimensioned to allow distributed contact with the monopile, and able to dampen the dynamics of the monopile and come radially into abutment against the monopile when it is introduced into the cage in order to stabilize and modify its inclination relative to the longitudinal axis of the cage;
• and
• the low portion of the cage comprises a plurality of blades extending along the longitudinal axis (X-X) of the cage and distributed around it, said blades being dimensioned to allow distributed contact with the monopile, able to come radially into abutment against the monopile when it is introduced into the cage in order to guide it during its descent into the cage and to modify its inclination relative to the longitudinal axis of the cage until reaching a sufficient soil resistance to naturally maintain the positioning in angle and in translation.