Petroleum and natural gas industries — Specific requirements for offshore structures — Part 4: Geotechnical and foundation design considerations
(ISO 19901-4:2016, MOD)
This part of ISO 19901 contains provisions for those aspects of geoscience and foundation engineering that are applicable to a broad range of offshore structures, rather than to a particular structure type. Such aspects are:
— site and soil characterization;
— identification of hazards;
— design and installation of shallow foundations supported by the seabed;
— design and installation of pile foundations;
— soil-structure interaction for auxiliary structures, e.g. subsea production systems, risers and flowlines (guidance given in A.10);
— design of anchors for the stationkeeping systems of floating structures (guidance given in A.11).
Particular requirements for marine soil investigations are detailed in ISO 19901-8.
Aspects of soil mechanics and foundation engineering that apply equally to offshore and onshore structures are not addressed. The user of this part of ISO 19901 is expected to be familiar with such aspects.
ISO 19901-4 outlines methods developed primarily for the design of shallow foundations with an embedded length (L) to diameter (D) ratio L/D < 1 (Clause 7) and relatively long and flexible pile foundations with L/D > 10 (Clause 8). This part of ISO 19901 does not apply to intermediate foundations with 1 < L/D < 10. Such intermediate foundations, often known as ‘caisson foundations’, comprise either shallow foundations with skirts penetrating deeper into the seabed than the width of the foundation, or shorter, more rigid and larger diameter piles than those traditionally used for founding offshore structures. The design of such foundations can require specific analysis methods; it is important that any extrapolation from the design methods described in this part of ISO 19901 to intermediate foundations be treated with care and assessed by a geotechnical specialist.