EN ISO 19901-4:2025

SLOVENSKI STANDARD
01-maj-2025
Industrija za predelavo nafte in zemeljskega plina - Posebne zahteve za naftne
ploščadi - 4. del: Obravnava geotehničnih značilnosti projektiranja (ISO 19901-
4:2025)
Petroleum and natural gas industries - Specific requirements for offshore structures -
Part 4: Geotechnical design considerations (ISO 19901-4:2025)
Erdöl- und Erdgasindustrie - Besondere Anforderungen an Offshore-Bauwerke - Teil 4:
Geotechnische und Fundament-Auslegungsmerkmale (ISO 19901-4:2025)
Industries du pétrole et du gaz naturel - Exigences spécifiques relatives aux structures
en mer - Partie 4: Bases conceptuelles géotechniques (ISO 19901-4:2025)
Ta slovenski standard je istoveten z: EN ISO 19901-4:2025
ICS:
75.180.10 Oprema za raziskovanje, Exploratory, drilling and
vrtanje in odkopavanje extraction equipment
93.020 Zemeljska dela. Izkopavanja. Earthworks. Excavations.
Gradnja temeljev. Dela pod Foundation construction.
zemljo Underground works
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 19901-4
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2025
EUROPÄISCHE NORM
ICS 75.180.10 Supersedes EN ISO 19901-4:2016
English Version
Oil and gas industries including lower carbon energy -
Specific requirements for offshore structures - Part 4:
Geotechnical design considerations (ISO 19901-4:2025)
Industries du pétrole et du gaz y compris les énergies à Öl und Gasindustrie einschließlich kohlenstoffarmer
faible teneur en carbone - Exigences spécifiques Energieträger-Besondere Anforderungen an Offshore-
relatives aux structures en mer - Partie 4: Bases Bauwerke-Teil 4: Geotechnische Auslegungsmerkmale
conceptuelles géotechniques (ISO 19901-4:2025) (ISO 19901-4:2025)
This European Standard was approved by CEN on 10 February 2025.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 19901-4:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 19901-4:2025) has been prepared by Technical Committee ISO/TC 67 "Oil and
gas industries including lower carbon energy" in collaboration with Technical Committee CEN/TC 12
“Oil and gas industries including lower carbon energy” the secretariat of which is held by NEN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by August 2025, and conflicting national standards shall
be withdrawn at the latest by August 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 19901-4:2016.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 19901-4:2025 has been approved by CEN as EN ISO 19901-4:2025 without any
modification.
International
Standard
ISO 19901-4
Third edition
Oil and gas industries including
2025-02
lower carbon energy — Specific
requirements for offshore
structures —
Part 4:
Geotechnical design considerations
Industries du pétrole et du gaz y compris les énergies à faible
teneur en carbone — Exigences spécifiques relatives aux
structures en mer —
Partie 4: Bases conceptuelles géotechniques
Reference number
ISO 19901-4:2025(en) © ISO 2025

ISO 19901-4:2025(en)
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
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or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 19901-4:2025(en)
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols and abbreviated terms. 4
4.1 Symbols for shallow and intermediate foundation design.4
4.2 Symbols for pile foundation design .6
4.3 Symbols for soil-structure interaction for auxiliary subsea structures, risers and
flowlines .9
4.4 Symbols for design of anchors for stationkeeping systems .10
4.5 Abbreviated terms . 12
5 General requirements .13
5.1 General . 13
5.2 Design cases and partial factors . 13
5.3 Representative and design values of geotechnical parameters .14
5.3.1 Guidelines .14
5.3.2 Determination of representative and design values of soil parameters .14
5.4 Reliability-based geotechnical design .16
5.5 Testing and instrumentation .16
6 Site investigation, identification of geohazards and carbonate soils . 17
6.1 General .17
6.2 Geological modelling and identification of hazards .17
6.2.1 General .17
6.2.2 Assessment of site geohazards .18
6.3 Carbonate soils .18
6.3.1 General .18
6.3.2 Characteristic features and properties of carbonate soils .18
6.3.3 Foundations in carbonate soils .18
7 Design of shallow and intermediate foundations for fixed structures . 19
7.1 General .19
7.2 Principles . 20
7.2.1 General principles . 20
7.2.2 Foundation embedment . 20
7.2.3 Sign conventions, nomenclature and action reference point .21
7.3 Acceptance criteria .21
7.3.1 Material and action factors .21
7.3.2 Use of partial factors in design . 22
7.4 Design considerations . 23
7.4.1 Adjusting for soil plug weight . 23
7.4.2 Skirt spacing. 23
7.4.3 Foundation base perforations .24
7.4.4 Skirtless foundations penetrating soft soils .24
7.4.5 Tensile stresses beneath foundations .24
7.4.6 Omni-directional actions .24
7.4.7 Interaction with other structures .24
7.4.8 Multiple foundations .24
7.4.9 Hydraulic stability . 25
7.4.10 Unconventional soils or soil profiles . 25
7.4.11 Selection of soil parameter values for design . 25
7.5 Ultimate limit state (stability) . 26
7.5.1 Assessment of bearing capacity of shallow foundations . 26

iii
ISO 19901-4:2025(en)
7.5.2 Assessment of sliding capacity of shallow foundations . 29
7.5.3 Assessment of capacity of intermediate foundations .31
7.6 Serviceability limit state (displacements and rotations) .32
7.6.1 General .32
7.6.2 Serviceability of shallow foundations under static loading .32
7.6.3 Serviceability of intermediate foundations. 34
7.6.4 Serviceability in response to dynamic and cyclic actions . 34
7.7 Alternative methods of design . 34
7.7.1 Yield surface approach . 34
7.7.2 Risk-informed decision making . 35
7.8 Installation . 35
7.8.1 General . 35
7.8.2 Skirt penetration resistance . 35
7.8.3 Required and allowable under-pressure . 36
7.9 Relocation, retrieval and removal .37
8 Pile foundation design .37
8.1 Pile capacity for axial compression.37
8.1.1 General .37
8.1.2 Axial pile capacity . 38
8.1.3 Skin friction and end bearing in clay soils . 39
8.1.4 Skin friction and end bearing in sands .41
8.1.5 Skin friction and end bearing in gravels .42
8.1.6 Skin friction and end bearing of grouted piles in rock .43
8.1.7 Skin friction and end bearing of driven piles in intermediate soils .43
8.2 Pile capacity for axial tension .43
8.3 Axial pile performance .43
8.3.1 Static axial behaviour of piles .43
8.3.2 Cyclic axial behaviour of piles . 44
8.4 Soil reaction for piles under axial actions . 44
8.4.1 Axial shear transfer t–z curves. 44
8.4.2 End bearing resistance–displacement, Q–z curve .45
8.5 Soil reaction for piles under lateral actions . 46
8.5.1 General . 46
8.5.2 Lateral soil reaction for clay .47
8.5.3 Lateral capacity for sand . 54
8.5.4 Lateral soil resistance – displacement p–y curves for sand . 55
8.5.5 p–y curves for fatigue actions for sands . 56
8.5.6 Refined assessment of lateral pile response .57
8.5.7 Lateral soil resistance-displacement curves in calcareous soil, cemented soil
and weak rock .57
8.6 Pile group behaviour .57
8.6.1 General .57
8.6.2 Axial behaviour .57
8.6.3 Lateral behaviour .57
8.7 Pile installation assessment . 58
8.7.1 General . 58
8.7.2 Drivability studies . 58
8.7.3 Obtaining required pile penetration .59
8.7.4 Driven pile refusal . .59
8.7.5 Pile refusal remedial measures .59
8.7.6 Selection of pile hammer and stresses during driving . 60
8.7.7 Use of hydraulic hammers .61
8.7.8 Drilled and grouted piles .62
8.7.9 Grouting pile-to-sleeve connections .62
8.7.10 Pile installation data .62
8.7.11 Installation of conductors and shallow well drilling . 63
9 Assessment of pile capacity for existing structures .63
9.1 General . 63

iv
ISO 19901-4:2025(en)
9.2 Geotechnical and foundation data . 64
9.2.1 Geotechnical data . 64
9.2.2 Design data . 64
9.2.3 Installation data . 64
9.2.4 Condition data . 64
9.2.5 Operational data . 65
9.3 Evaluation . 65
9.4 Assessment . 65
9.4.1 General . 65
9.4.2 Pushover response of pile foundation systems . 65
9.5 Time-dependent effects on pile foundations . 66
10 Geotechnical design input to subsea structures, risers and flowlines . 67
10.1 General .67
10.2 Geotechnical investigation .67
10.3 Foundations for subsea production structures .67
10.4 Steel catenary risers .67
10.4.1 General .67
10.4.2 Seabed characterisation . 68
10.4.3 Design for ultimate limit state . 68
10.4.4 Design for fatigue limit state . 68
10.5 Geotechnical design for jetted conductors and top tension risers .70
10.5.1 General .70
10.5.2 Jetted conductors .71
10.5.3 Soil-structure interaction for well integrity assessment . 73
10.5.4 Geotechnical input to well strength assessment . 73
10.5.5 Geotechnical input to well fatigue assessment .74
10.5.6 Geotechnical considerations in conductor driving analysis . 78
10.6 Foundation design for riser towers . 78
10.6.1 General . 78
10.6.2 Foundation options . 78
10.6.3 Loading actions and safety factors . 79
10.6.4 Design challenges . 79
10.7 Offshore pipelines and flowlines . 79
10.7.1 Geotechnical pipe-soil interaction (PSI) analysis . 79
10.7.2 Submarine slides and density flows: simulation and pipeline impact analysis . 80
11 Design of anchors for floating structures .81
Annex A (informative) Additional information and guidance .82
Bibliography .207

v
ISO 19901-4:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 67, Oil and gas industries including lower
carbon energy, Subcommittee SC 7, Offshore structures, in collaboration with the European Committee for
Standardization (CEN) Technical Committee CEN/TC 12, Oil and gas industries including lower carbon energy,
in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 19901-4:2016), which has been technically
revised.
The main changes are as follows:
— guidance extended on representative and design values for soil parameters (Clause 5);
— guidance added for geotechnical design of intermediate foundations for fixed structures and clause
renamed to ‘Design of shallow and intermediate foundations’ (Clause 7);
— requirements added on installation resistance, yield envelope approaches for ultimate limit state, and
performance- based design for shallow skirted and intermediate foundations (Clause 7);
— new unified CPT method for axial capacity in sands to replace the former main text method, new TZ
curve definition in sands, new unified CPT method for clays introduced into the Clause A.8, new PY curve
methodology for clays to replace the existing method (Clause 8);
— new requirements added on reassessment of pile capacity for existing structures (Clause 9);
— a new clause for pipelines, conductors and risers (Clause 10);
— references have been reviewed, updated and reduced where possible.
A list of all parts in the ISO 19901 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

vi
ISO 19901-4:2025(en)
Introduction
The International Standards on offshore structures prepared by TC 67 (i.e. ISO 19900, the ISO 19901 series,
ISO 19902, ISO 19903, ISO 19904-1, the ISO 19905 series, ISO 19906) constitute a common basis covering
those aspects that address design requirements and assessments of all offshore structures used by the
oil and gas industries worldwide. Through their application, the intention is to achieve reliability levels
appropriate for offshore structures, whatever the type of structure and the nature of the materials used.
Application specific requirements for different energy industries are given in the relevant standards. For
example, for the offshore wind industry, IEC 61400-1 and IEC 61400-3-1 outline the design requirements
(e.g. return periods) for offshore wind turbine support structures.
This document may be applied for the design of foundations used in the offshore wind industry. In this case,
it should be verified that the type and dimension of the foundation, as well as the type of actions acting
upon it, are consistent with those used in the development of the design methods. For example, the pile
design methods of Clauses 8 are not necessarily applicable to the design of monopiles for which L/D is less
than 10 and their validity for such cases should be assessed. Offshore wind structures can also have other
requirements, such as a characterisation of foundation stiffness, that are beyond the scope of this document.
Reference should be made to the overarching application specific codes and standards such as IEC 61400-3-1.
It is important to recognize that structural integrity is an overall concept comprising models for describing
actions, structural analyses, design rules, safety elements, quality of work, quality control procedures and
national requirements, all of which are mutually dependent. The modification of one aspect of design in
isolation can disturb the balance of reliability inherent in the overall concept or structural system. The
implications involved in modifications, therefore, should be considered in relation to the overall reliability of
all offshore structural systems.
For geotechnical design (engineering science dealing with the properties of soil: sand, silt, clay and rock),
some additional considerations apply. These include the time, frequency and rate at which actions are
applied, the method of installation, the properties of the surrounding soil, the overall behaviour of the
seabed, effects from adjacent structures and the results of drilling into the seabed. All of these, and any
other relevant information, should to be considered in relation to the overall reliability of the structure.
The International Standards on offshore structures prepared by TC 67 are intended to provide wide
latitude in the choice of structural configurations, materials and techniques without hindering innovation.
Geotechnical design practice for offshore structures has proved to be an innovative and evolving process
over the years. This evolution is expected to continue and is encouraged. Therefore, circumstances can arise
when the procedures described in this document or the International Standards on offshore structures
prepared by TC 67 (or elsewhere) are insufficient on their own to ensure that a safe and economical design
is achieved.
Seabed soils vary. Experience gained at one location is not necessarily applicable at another. Extra caution
is necessary when dealing with unconventional soils or unfamiliar foundation concepts. Sound engineering
judgment is therefore necessary in the use of this document.
Some background to and guidance on the use of this document is provided in Annex A.
ISO 19905 provides requirements and detailed guidance on foundations for mobile offshore units.
Figure 1 set outs a typical workflow for design of offshore foundations with reference to other relevant
International Standards.
vii
ISO 19901-4:2025(en)
NOTE Specific design and installation constraints can apply for structures in arctic regions (see ISO 19906), for
mobile offshore units, especially for jack-ups (see ISO 19905) and for anchors for floating units (see ISO 19901-7 Design
can be an iterative process from concept (initial feasibility and applicability study), basic to final design. Different
level of details and objectives are required in the various design stages.
Figure 1 — Flowchart showing typical design process for offshore foundations

viii
International Standard ISO 19901-4:2025(en)
Oil and gas industries including lower carbon energy —
Specific requirements for offshore structures —
Part 4:
Geotechnical design considerations
1 Scope
This document contains provisions for geotechnical engineering design that are applicable to a broad
range of offshore structures, rather than to a particular structure type. This document outlines methods
developed for the design of shallow foundations with an embedded length (L) to diameter (D) ratio L/D <
0,5, intermediate foundations, which typically have 0,5 ≤ L/D ≤ 10 (see Clause 7), and long and flexible pile
foundations with L/D > 10 (see Clauses 8 and 9).
This document also provides guidance on soil-structure interaction aspects for flowlines, risers and
conductors (see Clause 10) and anchors for floating facilities (see Clause 11). This document contains brief
guidance on site and soil characterization, and identification of hazards (see Clause 6).
This document can be applied for foundation design for offshore structures used in the lower carbon energy
industry.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 19900, Petroleum and natural gas industries — General requirements for offshore structures
ISO 19901-7, Oil and gas industries including lower carbon energy — Specific requirements for offshore
structures — Part 7: Station-keeping systems for floating offshore structures and mobile offshore units
ISO 19901-8, Oil and gas industries including lower carbon energy — Of
...