Structural Foundations

Introduction

The foundations are critical to the design of a structure. The foundation design has to cover a range of loading conditions:

Self Weight
Environmental
- Waves
- Water Current
Accidental loads
- Dropped Ojects
- Fishing Interaction
Operational loads
- Pipeline expansion
- Dynamic riser load

The foundation design is usually one of 2 types 'pile' or 'gravity based'.

Gravity based foundtaions generally considers 3 possible modes of failure:

Soil Bearing Pressure
Structure Sliding
Structure Overturning

Pile based foundations generally consider the following modes of failure:

Bearing Capacity
Pull-Out

Notable Projects

Project Name	Project Number	Notes
Wage Paladin	KW 694	CATS Tee Tie-In Structure
West DON & DON South West	KW 1009	Riser Base Structure Gravity Based Foundation, Multiple Headers Subsea Distribution Unit Protection Strucutre Pile Foundations, 'Fishing Friendly' design SSIV Protection Structure Gravity Based Foundation

Codes & Standards

Company	Title	Doc Number / Date
API		API-RP-2A

Books

Author	Title	Chapter

Related Subjects

Structural Global Analyses
Structural Appurtenances
Dropped Objects
Lifting
Weight Take Off

The calculations for the foundation capacity checks are a function of the loading, foundation size and soil parameters.

Skirts on gravity based foundations can be utilised to provide greater sliding resistance. The skirts penetrate into the soils and provide greater resistance to sliding. However, sometimes the full penetration of the skirts into the soils cannot be guaranteed.

The presence of a structure on the seabed affects the local flow of water in the vacinity. This results in a possibility of 'scour' occurring. For foundation design, 'scour' is considered as the movement of soils from the area where it is providing foundation support. Scour may be addressed by the use of a 'rip-rap', which acts as a cover for the soils, restricting the movement of soils in the area of foundations.