CSA Preface
This is the second edition of CAN/CSA-ISO 19901-4, Petroleum and natural gas industries — Specific requirements for offshore structures — Part 4: Geotechnical and foundation design considerations, which is an adoption without modification of the identically titled ISO (International Organization for Standardization) Standard 19901-4 (second edition, 2016-07-15). It supersedes the previous edition published in 2006 as CAN/CSA-ISO 19901-4 (adopted ISO 19901-4:2003). At the time of publication, ISO 19901-4:2016 is available from ISO in English only. CSA will publish the French version when it becomes available from ISO.
For brevity, this Standard will be referred to as CAN/CSA-ISO 19901-4 throughout.
This Standard specifies that the resistance of foundations be computed either by applying a material factor to the soil strength or a resistance factor to the foundation capacity. The methodologies are two variations of partial factor design and are accepted in different parts of the world. However, experience with design codes in Canada (in which both approaches have been tried and tested) has resulted in adoption of the resistance factor approach in general practice. Designers are encouraged to use the methods proposed in this Standard to harmonize Canadian and international practice. Adoption of material factors requires practitioners to use sound engineering judgment, precedent, and their own experience to obtain a similar design outcome.
Standards development within the Canadian Offshore Structures sector is harmonized with international standards development.
This Standard was reviewed for Canadian adoption by the harmonized Canadian Advisory Committee and CSA Technical Committee to ISO/TC 67/SC 7, Offshore Structures. This Standard has been formally approved by the CSA Technical Committee on Design, Construction, and Installation of Offshore Structures, under the jurisdiction of the CSA Strategic Steering Committee on Offshore Structures.
This Standard has been developed in compliance with Standards Council of Canada requirements for National Standards of Canada. It has been published as a National Standard of Canada by CSA Group.
Scope
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.
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