Appendix 5 Foundation Checks to Updated ISO Sections - 116C. 1. Introduction

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Lorena Andrea Griffin
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1 Appendix 5 Foundation Checks to Updated ISO Sections - 116C 1. Introduction Clauses 9 and A.9 of ISO have been significantly revised since the benchmarking work was commissioned. A key area of interest is the final geotechnical utilizations. This Appendix documents an additional work scope for the 116C rig where the utilizations using the updated Clauses 9 and A.9 for both the sand and clay foundations are reported as follows: Old ISO geotechnical utilizations New ISO geotechnical utilizations SNAME geotechnical utilizations Ratio of new ISO utilizations to SNAME utilizations (i.e. ISO/SNAME) Ratio of old ISO utilizations to SNAME utilizations (i.e. ISO/SNAME) Ratio of new ISO utilizations to old ISO utilizations (i.e. ISO new /ISO old) The global loading for the 116C sand case was reduced so that the new checks are closer to the yield surface. A copy of the revised Clauses 9 and A.9 to be used in the assessment was provided by the Benchmark Panel in an dated 11/8/ Aligned Reactions The tables below detail the reactions used. It is noted that the sand case reactions were modified while the clay case reactions remain the same and include the effect of p-y curves (which greatly reduces the horizontal loads on the footing). It is noted that the response analyses were performed assuming degrading moment fixity with constant linear vertical and horizontal springs and therefore Step 2b checks apply. Table A5.1 Leg Reactions 116C ISO Sand Case Storm heading ( o ) Leg ID BS Vertical Moment KN KN KN-m Bow 3,727 19,348 23,854 Port 3,721 18,766 23,897 Stbd 2,878 43,858 0 Bow 3,446 34,823 20,549 Port 3,201 11,766 20,047 Stbd 3,436 35,379 20,578

2 Table A5.2 Leg Reactions 116C ISO Clay Case Storm heading ( o ) Leg ID BS Vertical Moment KN KN KN-m Bow 72 25, ,022 Port 63 25, ,723 Stbd , ,368 Bow , ,276 Port , ,354 Stbd , , C ISO Sand Case Results The old and new ISO Sep 2b checks for sand are essentially the same as γ R,VH = 1,10 for partial embedment in both cases. The V-H envelope is shrunk towards the origin (F H = F V = 0) and the unit checks are calculated using for the origin of the vectors (F H = 0, F V = 0,5*Q V /γ R,VH ). The SNAME T&R 5-5A checks will differ in that the V-H envelope is shrunk towards the still water reaction point (F H = 0, F V = MN) and this same point is used as the origin of the vectors for the unity checks. The key parameters used in this case are the same for ISO and SNAME: Q V = 51.4 MN (see RPSE note, Appendix 2) Q H = 6.2 MN (see RPSE note, Appendix 2) Φ = 34 o, γ = 29 o, γ = 11 kn/m 3 (see RPSE note, Appendix 2) A s = 8.3 m 2 (Lateral Spudcan Area, partial penetration) k a = Tan 2 (45 o - Φ /2) = k p = 1/K a = h 1 = 0; h 2 = 2.7m (penetration to tip) Unfactored V-H envelopes for sand: Bearing: [F H / Q H ] 4 [F V / Q V ] [1 F V / Q V ] = 0 Sliding: F H = F V tan (γ) γ (k p k a ) (h 1 + h 2 ) A s Figure A5.1 shows the V-H envelopes as well as the leg reactions from Table A5.1. It can be seen that the maximum vertical leg reaction (leeward leg in 60 deg environment) exceeds the factored bearing capacity envelope.

3 F V (MN) Leg Reaction -60 Deg Head Leg Reaction -120 Deg Head Origin -ISO Origin SNAME Unfactored Factored SNAME Factored ISO 0 F H (MN) Figure A5.1 V-H Envelopes for Sand Case

4 Table A5.3 summarizes the unity checks obtained. It is noted that all ISO UCs are vectorial while the SNAME sliding UC is: BS / (0.8*Q H ). Table A5.3 Summary of Unity Checks 116C Sand New ISO / Old ISO / New ISO Old ISO New ISO SNAME SNAME SNAME / Old ISO Bearing Sliding A Step 3 check was performed and an additional settlement of 5cm would be sufficient to accommodate the maximum leg vertical reaction, which is acceptable. The rig therefore meets all the necessary foundation checks for the reduced environment considered in this Appendix. The ISO checks for sand appear to be more penalizing than those of SNAME for this sand case C ISO Clay Case Results The old and new ISO Sep 2b checks for clay use the same V-H unfactored envelope but shrunk to different origins. The new ISO envelope is shrunk towards the origin (FH = 0; FV = WBF,o - BS), while the old ISO envelope was shrunk towards the origin (FH = 0; FV = 0). In both cases the bearing capacity unit checks use for the origin of the vectors F H = 0 and F V = 0,5*Q V /γ R,VH. However, γ R,VH for full embedment was 1,15 in the old version and now is 1,10. In both cases the sliding unity check is F H Q H / γ R,Hfc, where γ R,Hfc = The key parameters for the ISO checks are: Q V = 64.4 MN (see RPSE note, Appendix 2) Q Vnet = 48.0 MN (see RPSE note, Appendix 2) Q H = 16.2 MN (see RPSE note, Appendix 2) A s = 50.4 m 2 (see RPSE note, Appendix 2) A = m 2 (see RPSE note, Appendix 2) B = 13.5 m (see RPSE note, Appendix 2)

5 D = 25.6 m (see RPSE note, Appendix 2) a = D /2.5B = 0.76 W BF,o - B S = MN (see RPSE note, Appendix 2) Origin: F V = 0,5*Q V /γ R,VH = MN Unfactored V-H envelopes for clay in ISO: Bearing: [F H / Q H ] 2 16 (1 - a) [F V / Q V ] 2 [1 F V / Q V ] 2 4 a [F V / Q V ] [1 F V / Q V ] = 0 Sliding: F H = Q H The SNAME Sep 2b checks for clay use an unfactored bearing capacity envelope formulation that is shrunk towards the still water reaction (F H = 0; F V = MN). The unit checks are calculated using for the origin this same still water reaction. It is noted that SNAME has a much lower horizontal capacity as deep penetration effects are not considered. The key parameters for the SNAME checks are: Q V = 64.2 MN (see RPSE note, Appendix 2) Q H = 8.6 MN (see RPSE note, Appendix 2) A s = 50.4 m 2 (see RPSE note, Appendix 2) A = m 2 (see RPSE note, Appendix 2) B = 13.5 m (see RPSE note, Appendix 2) D = 24.4 m (see RPSE note, Appendix 2) a = D /2.5B = Origin: F V = MN Figure A5.2 shows the V-H envelopes as well as the leg reactions from Table A.5.2. It can be seen that the maximum vertical leg reaction (leeward leg in 60 deg environment plus MN of backflow and infilling during preload) approaches but does not exceed the factored bearing capacity envelopes. It is noted that by coincidence the origin for the unity checks in the ISO New checks and SNAME checks has similar numeric values: MN and MN respectively.

6 F V (MN) Leg Reaction -60 Deg Head Leg Reaction -120 Deg Head Origin -ISO New and SNAME Backflow / Infill Weight Origin -ISO Old Unfactored - ISO Factored SNAME Factored -ISO New Unfactored SNAME Factored -ISO Old 5.00 F H (MN) Figure A5.2 V-H Envelopes for Clay Case Table A5.4 summarizes the unity checks obtained. The rig meets all the necessary foundation checks. The bearing capacity checks for ISO and SNAME appear reasonably similar for this clay case. The sliding checks in ISO are much more favorable than in SNAME in this clay case due to much greater horizontal capacity arising from deep penetration corrections included in ISO but not in SNAME.

7 Table A5.4 Summary of Unity Checks 116C Clay New ISO / Old ISO / New ISO / Old ISO New ISO SNAME SNAME SNAME Old ISO Bearing Sliding

Design of pile foundations following Eurocode 7-Section 7

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