Gravity-based structure

A gravity based structure for supporting offshore installations, the gravity based structure comprising:

• a foundation comprising:
• a basal portion comprising:
• a wall extending upwardly from the basal portion, said wall forming an outer boundary of a cavity;
• a slab defining a lower boundary of said cavity, said slab having a top surface and a bottom surface and including a portion extending outside a bottom edge of the wall;
• a plurality of channels, each channel of the plurality of channels formed through said portion of the slab extending outside the bottom edge of the wall and each channel of the plurality of channels extending from the bottom surface of the slab to the top surface of the slab, each channel of the plurality of channels comprising a first opening formed through the bottom surface of the slab and open to water surrounding the slab and a second opening formed through the top surface of the slab and open to water surrounding the slab, said plurality of channels acting as drainage channels to reduce pore pressure build-up under said slab, the top surface of the portion of the slab extending outside the bottom edge of the wall being in direct contact with water surrounding an exterior of the gravity based structure;
• and
• wherein at least one first layer of filter material, with a gradation suitable for draining water entrapped beneath the basal portion, is installed on a seabed beneath the foundation.