ABS 248-2017 GUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND PLATE ANCHORS.pdf

1、Guidance Notes on Design and Installation of Drag Anchors and Plate Anchors GUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND PLATE ANCHORS MARCH 2017 American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 2017 American Bureau of Shipping. All rights

2、 reserved. ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Foreword Foreword These Guidance Notes provide ABS recommendations for the design and installation of drag anchors and plate anchors for offshore service. Included in these Guidance Notes are the site investigation, methodologies for

3、geotechnical design and structural assessment, and installation and testing recommendations for drag anchors and plate anchors. Other approaches that can be proven to produce at least an equivalent level of safety will also be considered as an alternative. These Guidance Notes are applicable to the

4、design of drag anchors and plate anchors, as a component of taut, semi-taut, or catenary mooring systems. These Guidance Notes are to be used with the criteria contained in the ABS Rules for Building and Classing Offshore Installations, the ABS Rules for Building and Classing Floating Production Ins

5、tallations, the ABS Guide for Building and Classing Floating Offshore Wind Turbine Installations, and the ABS Rules for Building and Classing Mobile Offshore Drilling Units. These Guidance Notes become effective on the first day of the month of publication. Users are advised to check periodically on

6、 the ABS website www.eagle.org to verify that this version of these Guidance Notes is the most current. We welcome your feedback. Comments or suggestions can be sent electronically by email to rsdeagle.org. Terms of Use The information presented herein is intended solely to assist the reader in the

7、methodologies and/or techniques discussed. These Guidance Notes do not and cannot replace the analysis and/or advice of a qualified professional. It is the responsibility of the reader to perform their own assessment and obtain professional advice. Information contained herein is considered to be pe

8、rtinent at the time of publication, but may be invalidated as a result of subsequent legislations, regulations, standards, methods, and/or more updated information and the reader assumes full responsibility for compliance. This publication may not be copied or redistributed in part or in whole witho

9、ut prior written consent from ABS. ii ABSGUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND PLATE ANCHORS .2017 Table of Contents GUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND PLATE ANCHORS CONTENTS SECTION 1 General 1 1 Introduction . 1 3 Scope and Application 1 5 Terms a

10、nd Definitions . 1 7 Symbols and Abbreviation 1 7.1 Symbols . 1 7.3 Abbreviations . 4 SECTION 2 Site Investigation . 5 1 General . 5 3 Desk Study 5 5 Sea Floor Survey 6 7 Subsurface Investigation and Testing . 6 7.1 Subsurface Investigations . 6 7.3 Soil Testing Program . 7 SECTION 3 Drag Anchor . 8

11、 1 Introduction . 8 3 Installation Performance . 8 5 Holding Capacity . 9 5.1 Empirical Method . 10 5.3 Analytical Method Based on Limit Equilibrium Principle 10 5.5 Finite Element Method. 10 5.7 Post Installation Effect . 10 5.9 Uplift Angle 10 FIGURE 1 Skematic of Drag anchor 8 FIGURE 2 Drag Treje

12、ctory of Drag anchor 9 SECTION 4 Plate Anchor . 11 1 Introduction . 11 3 Installation Performance . 13 3.1 General 13 3.3 VLA . 14 ABSGUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND PLATE ANCHORS .2017 iii 3.5 SEPLA . 14 3.7 DEPLA . 15 5 Holding Capacity . 15 FIGURE 1 Schematic of SEPL

13、A . 11 FIGURE 2 Installation Process for Suction Embedded Plate Anchor 12 FIGURE 3 Installation Process of DEPLA 13 SECTION 5 Commentary on Structural Assessment 17 1 General . 17 3 Yielding Check 17 5 Fatigue Assessment . 17 7 Anchor Reverse Catenary Line . 17 9 Buckling Assessment 17 SECTION 6 Anc

14、hor Installation . 18 1 General . 18 3 Installation Monitoring . 18 APPENDIX 1 Analytical Method for Drag Anchor Design and Design Procedure Recommendation . 19 1 General . 19 3 Analytical Model 19 3.1 Anchor Holding Capacity Under Combined Load 19 3.3 Kinematic Behavior 21 3.5 Embedded Anchor Line

15、Equilibrium Equation . 22 5 Simplified Analysis for Trajectory Prediction . 23 7 Procedure 23 9 Recommended Design Procedure 24 11 Work Example . 25 11.1 Design Parameters 25 11.3 Predicted Anchor Trajectory and Holding Capacity . 26 11.5 Anchor Design . 26 TABLE 1 Values of Interaction Coefficient

16、. 21 TABLE 2 Design Parameter for Drag Anchor Trajectory Prediction 26 FIGURE 1 Drag Anchor Definition 20 FIGURE 2 Flowchart for Drag Anchor Trajectory Prediction 24 FIGURE 3 Design Procedure for Drag Anchor Trajectory Prediction . 25 FIGURE 4 Anchor Trajectory Prediction during Drag Embedment 27 FI

17、GURE 5 Anchor Tension during Drag Embedment 27 FIGURE 6 Fluke Angle during Drag Embedment . 27 iv ABSGUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND PLATE ANCHORS .2017 APPENDIX 2 Cyclic Loading Effect . 28 1 General . 28 3 Cyclic Shear Strength . 28 5 Procedure . 29 5.1 Design Storm C

18、omposition and Cycle Counting 29 5.3 Equivalent Number of Cycles to Failure 30 5.5 Cyclic Contour Diagram. 30 5.7 Description of Procedure . 30 FIGURE 1 Typical Cyclic Shear Stress 28 FIGURE 2 Example of Transformation of Cyclic Loading History to Constant Cyclic Parcels 30 APPENDIX 3 Set-up Effect

19、. 32 APPENDIX 4 Capacity Factor for Plate Anchors in Cohesive Soil . 33 1 Capacity Factor in Soil with Constant Shear Strength with Depth . 33 3 Capacity Factor in Soil with Linearly Increasing Shear Strength 34 5 Capacity Factor in Layered Soil 34 FIGURE 1 Capacity Factor for Soil with Constant She

20、ar Strength 33 FIGURE 2 Capacity Factor for Soil with Linearly Increasing Shear Strength . 34 APPENDIX 5 Loss of Embedment During Keying for SEPLA . 35 APPENDIX 6 Methodology to Calculate the Anchor Reverse Catenary Line 36 1 General . 36 3 Equilibrium Equations of Embedded Anchor Line 37 5 Simplifi

21、ed Solution for the Mooring Catenary Line . 38 7 Description of Procedure 40 9 Work Example . 41 TABLE 1 Effective Surface and Bearing Area for Anchor Line 38 TABLE 2 Parameters for the Work Example 41 FIGURE 1 General Arrangement of Anchor Line for Plate Anchor 36 FIGURE 2 Force Equilibrium of Anch

22、or Line Element . 37 FIGURE 3 Soil Strength Adjustment to Account for Anchor Line Weight . 40 FIGURE 4 Anchor Line Profile for the Work Example 41 ABSGUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND PLATE ANCHORS .2017 v APPENDIX 7 Commentary on Acceptance Criteria 42 1 General . 42 3 F

23、actor of Safety for Drag anchor 42 5 Factor of Safety for Plate Anchor 43 7 Acceptance Criteria for Yielding 44 9 Acceptance Criteria for Fatigue 44 TABLE 1 Factor of Safety for Drag anchor Holding Capacities . 42 TABLE 2 The Coefficient of Friction for Mooring Line 43 TABLE 3 Factor of Safety for P

24、late Anchor 43 APPENDIX 8 References 45 vi ABSGUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND PLATE ANCHORS .2017 Section 1: Introduction SECTION 1 General 1 Introduction The purpose of these Guidance Notes is to provide recommendations for the design and installation of drag anchors a

25、nd plate anchors for taut, semi-taut or catenary mooring systems. These Guidance Notes are to be used in conjunction with the ABS Rules for Building and Classing Offshore Installations (OI Rules), the ABS Rules for Building and Classing Floating Production Installations (FPI Rules), the ABS Guide fo

26、r Building and Classing Floating Offshore Wind Turbine Installations (FOWTI Guide), and the ABS Rules for Building and Classing Mobile Offshore Drilling Units (MODU Rules). 3 Scope and Application These Guidance Notes cover the geotechnical design, structural assessment and installation for both dra

27、g anchors and plate anchors. 5 Terms and Definitions DIP follower: The dynamically installed pile (DIP) used to install the dynamically embedded plate anchor (DEPLA) by self-weight penetration. Embedment ratio: The ratio of anchor embedment depth to the width of anchor fluke. Keying: The process tha

28、t a plate anchor is pulled and rotated until the plate surface is perpendicular to the load direction to achieve the maximum capacity. Loss of embedment: Vertical displacement at the center of the anchor fluke during keying. Soil overburden pressure: The pressure caused by the soil self-weight. It i

29、s defined as the soil unit weight times the anchor embedment depth. Soil non-homogeneity: A non-dimensional factor to represent the non-homogeneity of the soil. It is defined as the rate of increasing undrained shear strength with depth time the width of the anchor fluke divided by the soil undraine

30、d shear strength (kB/su). Suction follower: The suction caisson that used to penetrate the plate anchor and can be reused to install the suction embedded plate anchor. Thickness ratio: The ratio of plate anchor fluke width to thickness. 7 Symbols and Abbreviation 7.1 Symbols Af= area of the anchor f

31、luke Aplate= projected maximum fluke area perpendicular to the direction of pullout Ain= plan view of inside area where suction pressure is applied Ainside= inside lateral area of the suction follower Awall= sum of inside and outside wall area embedded into soil Atip= vertical projected sectional ar

32、ea for both suction follower and plate anchor ABSGUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND PLATE ANCHORS .2017 1 Section 1 General B = width of the plate b = chain bar or wire diameter d = nominal diameter of chain, or diameter of wire or rope. D = outside diameter of the suction

33、 follower Dwater= water depth e = loading eccentricity ef= loading eccentricity for friction resistance ew= loading eccentricity for anchor weight Et= multipliers to give the effective widths in the tangential direction En= multipliers to give the effective widths in the normal direction F = resista

34、nce offered by the soil tangential to the chain (per unit length) Ffriction= friction of mooring line on the sea bed fs= anchor shank resistance fsl= frictional coefficient of mooring line on sea bed at sliding Fanchor= maximum load at anchor for design environmental condition FOS = factor of safety

35、 k = rate of increasing of undrained shear strength with depth L = length of the plate Lbed= length of mooring line on seabed at the design storm condition M0= initial moment corresponding to zero net vertical load on the anchor Nc= bearing capacity factor Ne= bearing capacity factor under combined

36、loading Nq= bearing capacity factor, depending on the friction angle Nn,max= bearing capacity factor under condition of pure normal loading Nt,max= bearing capacity factor under condition of pure tangential loading Nm,max= bearing capacity factor under condition of pure moment loading Pline= maximum

37、 mooring line tension Q = resistance offered by the soil normal to the chain (per unit length) Qave= average bearing resistance per unit length of chain over the soil depth D Q1= normalized soil resistance due to mudline strength Q2= normalized soil resistance due to strength gradient Qtot= total pe

38、netration resistance Ranchor= holding capacity of drag anchor RPLA= holding capacity of plate anchor s = distance measured along the chain 2 ABSGUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND PLATE ANCHORS .2017 Section 1 General su= undrained shear strength of soil at the depth of anc

39、hor fluke AVEtipus = average of triaxial compression, triaxial extension, and direct simple shear (DSS) undrained shear strength at anchor tip level, DSSus = direct simple shear strength su,r= remolded undrained shear strength su0= undrain shear strength at mudline St= soil sensitivity t = thickness

40、 of the anchor fluke T = tension of the chain Ta= tension at the attachment point T0= tension at the mudline T* = normalized tension = coefficient w = anchor line self-weight per unit length Wsub= submerged unit weight of mooring line W = submerged weight during installation aW = difference between

41、the anchor weight in air and the anchor buoyancy force in soil x = horizontal length of the mooring line from anchor x* = x/D z = loss of anchor embedment z = anchor embedment depth z = embedment depth of the mooring line from the mudline z* = z/D ztip= tip penetration depth ins= adhesion factor dur

42、ing installation, it is usually defined as the ratio of remolded shear strength over undisturbed shear strength = adhesion factor for anchor line = effective unit weight of soil = soil unit weight = reduction for soil disturbance due to penetration and keying eqv= equivalent Von Mises stress yield=

43、yield stress of the considered anchor structural component = load inclination during the keying a= average shear stress cy= cyclic shear stress amplitude ABSGUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND PLATE ANCHORS .2017 3 Section 1 General f,cy= cyclic shear strength 0= initial so

44、il shear stress prior to the installation of anchor = orientation of the chain to the horizontal a= anchor line angle from horizontal at shackle point f= fluke angle to horizontal 0= angle of anchor line from horizontal at mudline = interface friction angle at soil-mooring line interface 7.3 Abbrevi

45、ations CPTU piezocone penetrometer test DEC Design Environmental Condition DEPLA dynamically embedded plate anchor DIP dynamically installed pile DSS direct simple shear SEPLA suction embedded plate anchor VLA vertical loaded anchor 4 ABSGUIDANCE NOTES ON DESIGN AND INSTALLATION OF DRAG ANCHORS AND

46、PLATE ANCHORS .2017 Section 2: Site Investigation SECTION 2 Site Investigation 1 General Site investigation is conducted to determine the seabed stratigraphy and soil engineering parameters for the anchor design and geohazards analysis. Generally, the procedure for the site investigation program sho

47、uld include: Desk study to obtain regional and relevant data for the site Sea floor survey to obtain relevant geophysical data Subsurface investigation and test to obtain the necessary geotechnical data Additional sea floor survey and/or subsurface investigation and/or laboratory test as required De

48、pending on the size of a project and/or the complexity of the geotechnical context and associated risks (geohazards), additional intermediate stages may be necessary. The site investigation should satisfy the requirements given in 3/6.3 of the OI Rules. It is important that the geophysical and geote

49、chnical components are planned together as integrated parts of the same investigation. Data analyses should be considered as a single exercise drawing together with the results of geological, geophysical, hydrographic and geotechnical work, performed by specialists, in an integrated manner into one final report. 3 Desk Study The desk study assembles existing data for the preliminary site assessment and will formulate requirements for subsequent sea floor surveys and subsurface investigations. The desk study should include a review of all sources of ap