The nature of the sea bed soils, its susceptibility to local erosion and bed sand wave movement has a large influence on base type. Established and developing foundation systems can be applied to produce efficient solutions

Gravity Bases
Stiff Clay or Rock :
Precast Base
Jacks and Grout Bases

gravity baseThe system can be automated for levelling, grouting and jack removal

Grout Bag foundations have the following advantages over pre-levelled stone beds :-
• Reduced number of marine plant operations
• Not prone to wash out
• Not prone to settlement
• Not prone to dynamic compaction and suffusion
• Contact to base soffit is intimate

See Confederation Bridge Foundations (B67) for a similar system example and “Foundations to Precast Marine Structures” Hawkswood M.G. & Allsop N.W.H. (2009) for further reading.

Sand and Clays :
Precast Base / Skirt
Grout Bags

gravity base with skirtBase installation can be automated. The base can be levelled by barge control, jacks or by initial pumping into levelling grout bags in skirted pods

Skirted system advantages :-
• Level bed not required
• Immediate edge scour protection
• Excavation for embedment reduced
• Backfill surcharge saved

Suction Caisson Bases
Sand and Soft / Firm Clay:
Steel or Precast Suction Caisson Base
Grout Bag Infill Contact

suction caissonBase installation is automated with prefixed suction pumping hoses, grout hoses and prefixed infill grout bags to ensure contact on uneven beds. Vertical control can be provided by barge control or differential suction pumping into skirted suction pods.

Suction caisson bases have the prospect of :-

• Embedment without excavation
• Entrap a large soil weight to resist overturning
• Higher ground bearing/ reduced settlement
• Scour protection by rosk dumping

Past Projects

Suction Wind Turbine Bases (B94)