1、Geotechnical and Foundation Design ConsiderationsANSI/API RECOMMENDED PRACTICE 2GEOFIRST EDITION, APRIL 2011ADDENDUM 1, OCTOBER 2014ISO 19901-4:2003 (Modified), Petroleum and natural gas industriesSpecific requirements for offshore structures, Part 4Geotechnical and foundation design considerationsG
2、eotechnical and Foundation Design ConsiderationsUpstream SegmentANSI/API RECOMMENDED PRACTICE 2GEOFIRST EDITION, APRIL 2011ADDENDUM 1, JULY 2014ISO 19901-4:2003 (Modified), Petroleum and natural gas industriesSpecific requirements for offshore structures, Part 4Geotechnical and foundation design con
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16、I standards are reviewed and revised, reaffirmed, or withdrawn at least every five years. A one-timeextension of up to two years may be added to this review cycle. Status of the publication can be ascertained from theAPI Standards Department, telephone (202) 682-8000. A catalog of API publications a
17、nd materials is publishedannually by API, 1220 L Street, NW, Washington, DC 20005.Suggested revisions are invited and should be submitted to the Standards Department, API, 1220 L Street, NW,Washington, DC 20005, standardsapi.org.iiiiii Contents Page Foreword vi Introduction . vii 1 Scope 1 2 Normati
18、ve references 1 3 Terms and definitions . 1 4 Symbols 2 4.1 General . 2 4.2 Symbols for stability of shallow foundation . 2 4.3 Symbols for pile foundation design 5 5 General requirements . 7 5.1 General . 7 5.2 Testing and instrumentation 7 5.3 Conductor installation and shallow well drilling 8 6 G
19、eotechnical data acquisition and integrated geoscience studies . 8 6.1 Geotechnical assessment 8 6.2 Shallow geophysical investigation 9 6.3 Geological modelling and identification of hazards 9 6.3.1 General . 9 6.3.2 Earthquakes . 10 6.3.3 Fault planes 10 6.3.4 Seafloor instability 10 6.3.5 Scour a
20、nd sediment mobility . 10 6.3.6 Shallow gas 11 6.3.7 Seabed subsidence . 11 6.4 Geotechnical investigation . 11 6.4.1 General . 11 6.4.2 Soil investigation and testing . 12 6.4.3 Identification and classification of soils and rocks . 13 6.4.4 Carbonate soils 13 7 Stability of shallow foundations 13
21、7.1 General . 13 7.2 Principles 14 7.3 Acceptance criteria . 14 7.3.1 General . 14 7.3.2 Variations in safety factor . 14 7.3.3 Use in design . 15 7.3.4 Alternative method of design based on yield surfaces . 18 7.4 Undrained bearing capacity constant shear strength with depth . 18 7.5 Undrained bear
22、ing capacity linearly increasing shear strength 19 7.6 Drained bearing capacity 19 7.7 Shear strength used in bearing capacity calculations 21 7.8 Response of shallow foundations to static and pseudo-static loading 22 7.8.1 Short-term displacement (undrained loading) . 22 7.8.2 Long-term displacemen
23、t (primary settlement) . 23 7.8.3 Long-term displacement (secondary settlement) 23 7.8.4 Long-term displacement (regional) . 23 7.9 Response of shallow foundations to environmental loading . 23 7.10 Hydraulic stability 24 7.10.1 Scour . 24 7.10.2 Piping 24 iv 7.11 Installation and removal . 24 7.12
24、Shallow foundations equipped with seabed penetrating skirts 24 7.13 Shallow foundations without seabed penetrating skirts 25 7.14 Installation effects 25 7.15 Sliding stability . 25 7.15.1 General . 25 7.15.2 Surface foundations . 25 7.16 Torsional stability . 26 8 Pile foundation design . 26 8.1 Pi
25、le capacity for axial compression 26 8.1.1 General . 26 8.1.2 Ultimate axial pile capacity 27 8.1.3 Shaft friction and end bearing in cohesive soils . 27 8.1.4 Shaft friction and end bearing in cohesionless soils . 29 8.1.5 Shaft friction and end bearing of grouted piles in rock 31 8.2 Pile capacity
26、 for axial pullout loads 31 8.3 Axial pile performance . 32 8.3.1 Static axial behavior of piles . 32 8.3.2 Cyclic axial behavior of piles . 32 8.4 Soil reaction for piles under axial compression 32 8.4.1 General . 32 8.4.2 Axial shear transfer t-z curves . 32 8.4.3 End bearing resistance-displaceme
27、nt, Qz, curve 34 8.5 Soil reaction for piles under lateral loads 35 8.5.1 General . 35 8.5.2 Lateral capacity for soft clay . 36 8.5.3 Lateral soil resistancedisplacement p-y curves for soft clay . 36 8.5.4 Lateral capacity for stiff clay . 38 8.5.5 Lateral soil resistanceDisplacement (p-y) curves f
28、or stiff clay 38 8.5.6 Lateral capacity for sand . 38 8.5.7 Lateral soil resistanceDisplacement (p-y) curves for sand 39 8.6 Pile group behavior 40 8.6.1 General . 40 8.6.2 Axial behavior . 40 8.6.3 Lateral behavior 40 9 Soil-structure interaction for risers, flowlines and auxiliary subsea structure
29、s . 41 9.1 Site characterization . 41 9.1.1 General considerations 41 9.1.2 Desktop assessment of site conditions . 41 9.1.3 Shallow high resolution geophysical survey . 41 9.1.4 Geotechnical investigation 42 9.1.5 Integrated study 43 9.2 Steel catenary risers . 43 9.2.1 Introduction . 43 9.2.2 Desi
30、gn for ultimate limit state . 43 9.2.3 Design for fatigue . 44 9.2.4 Seabed-riser response in vertical plane . 44 9.2.5 Trenching . 48 9.2.6 Three-dimensional motion . 49 9.3 Top tension riser . 49 9.3.1 Introduction . 49 9.3.2 Soil response 50 9.3.3 Development of p-y springs via finite element (FE
31、) analyses 51 9.3.4 Additional considerations 52 9.3.5 Summary and recommendations for top tension risers . 53 9.4 Riser tower foundations . 53 9.4.1 Introduction . 53 9.4.2 Foundation options 53 9.4.3 Loads and safety factor 53 9.4.4 Soil design parameters 54 9.4.5 Design issues 54 v 9.4.6 Inspecti
32、on and monitoring . 56 9.5 Flowlines and pipelines 56 9.5.1 Introduction 56 9.5.2 Loads on seabed pipelines . 56 9.5.3 Soil reaction forces . 56 9.5.4 Analysis of pipeline-soil interaction 57 Annex A (informative) Additional information and guidance . 60 Annex B (informative) Carbonate soils . 85 An
33、nex C (informative) Pile foundation design commentary . 88 Bibliography 109 vi 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 I
34、SO 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
35、closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards.
36、Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this d
37、ocument may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 19901-4 was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore structures for petroleum, petrochemical and natural gas industries, Subcommittee
38、SC 7, Offshore structures. ISO 19901 consists of the following parts, under the general title Petroleum and natural gas industries Specific requirements for offshore structures: Part 1: Metocean design and operating considerations Part 2: Seismic design procedures and criteria Part 3: Topsides struc
39、ture Part 4: Geotechnical and foundation design considerations Part 5: Weight control during engineering and construction Part 6: Marine operations Part 7: Stationkeeping systems for floating offshore structures and mobile offshore units ISO 19901 is one of a series of standards for offshore structu
40、res. The full series consists of the following International Standards. ISO 19900, Petroleum and natural gas industries General requirements for offshore structures ISO 19901 (all parts), Petroleum and natural gas industries Specific requirements for offshore structures ISO 19902, Petroleum and natu
41、ral gas industries Fixed steel offshore structures ISO 19903, Petroleum and natural gas industries Fixed concrete offshore structures ISO 19904, Petroleum and natural gas industries Floating offshore structures ISO 19905-1, Petroleum and natural gas industries Site-specific assessment of mobile offs
42、hore units Part 1: Jack-ups ISO/TR 19905-2, Petroleum and natural gas industries Site-specific assessment of mobile offshore units Part 2: Jack-ups commentary ISO 19906, Petroleum and natural gas industries Arctic offshore structures vii Introduction The API offshore structures standards constitute
43、a common basis covering those aspects that address design requirements and assessments of all offshore structures used by the petroleum and natural gas industries worldwide. Through their application the intention is to achieve reliability levels appropriate for manned and unmanned offshore structur
44、es, whatever the type of structure and the nature of the materials used. It is important to recognize that structural integrity is an overall concept comprising models for describing actions, structural analyses, design rules, safety elements, workmanship, quality control procedures and national req
45、uirements, 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, need to be considered in relation to the overall r
46、eliability of all offshore structural systems. The offshore structures International Standards are intended to provide a wide latitude in the choice of structural configurations, materials and techniques without hindering innovation. Sound engineering judgment is therefore necessary in the use of th
47、ese International Standards. The overall concept of structural integrity is described above. For foundations, some additional considerations apply. These include the time, frequency and rate at which actions are applied, the method of foundation installation, the properties of the surrounding soil,
48、the overall behavior of the seabed, effects from adjacent structures and the results of drilling into the seabed. All of these, and any other relevant information, need to be considered in relation to the overall reliability of the foundation. The design practice for the foundations of offshore stru
49、ctures has proved to be an innovative and evolving process over the years since the 1950s. This evolution is expected to continue and is encouraged. Therefore, circumstances can arise when the procedures described herein (or elsewhere) are insufficient on their own to ensure that a safe and economical foundation design is achieved. Seabed soils vary. Experience gained at one location is not necessarily applicable at another. The scope of the site investigation for one structure is not necessarily adequate for another. Extra c
