Case 2: Bucket foundation - NGI

Application of a cyclic accumulationmodel for undrained and partially drainedgeneral boundary value problemsPart 2: ApplicationsAna Pageana.page@ngi.no

ApplicationsComparison of the performance of UDCAM and PDCAMwith some simplified approachesCase 1: Monopile foundationCase 2: Bucket foundation2of 20

Case 1: Monopile foundationJoint study betweenGS E&CNGIObjective: see the effect of usingmore advanced models instead of p-ycurves in the behaviour of a monopileDisplacement and rotationof the monopileunder SLS conditionHorizontal displacements3of 20

Case 1: Monopile foundationSoil stratigraphy (Korean West Sea)d = 5.2 mL = 37 mLooseSandPDCAMNCClayUDCAM4of 20

Case 1: Monopile foundationUDCAM & PDCAM:Software:PLAXIS 3D FoundationCyclic shearstrain>5%4%3%2%1%0%5of 20

Case 1: Monopile foundationRotation < 1°6of 20

Case 1: Monopile foundationSandClaySandClayIn clay:The stiffness is higher inUDCAM than in the p-ycurvesIn sand:The stiffness is lower forPDCAM than for the p-ycurvesSand7of 20

ApplicationComparison of the performance of UDCAM and PDCAMwith some simplified approachesCase 1: Monopile foundationCase 2: Bucket foundation8of 20

Case 2: Bucket foundationSimplified approach vs. PDCAMSimplified conditionsMore realistic conditionsCompare:• N eq• the accumulated pore pressureH cyFor the same cyclic load historySand9of 20

Case 2: Bucket foundationSimplified conditionsAssumptions:Linear-elastic soilPore pressuresgenerated onlybelow the bucketOnly radial disipationThe cyclic degradation is evaluated in one representative point10 of 20

Case 2: Bucket foundationSimplified approachPore Pressure Countour DiagramHcy100%u p,norm = 1.00.90.80.5Number of cycles0.250.10.05N eq = 1211 of 20

Case 2: Bucket foundationSimplified approachHcyu p,norm = 1.00.950%Number of cycles0.80.50.250.10.05N eq = 1012 of 20

Case 2: Bucket foundationSimplified approachu p,norm = 1.00.90.80.50.250.10.0513 of 20

Case 2: Bucket foundationPDCAM: Simplified conditionsu p,norm = 1.00.90.80.50.250.10.05N eq = 9Equivalent number of cycles, N eq1 4 7 10 1314 of 20

Case 2: Bucket foundationSimplified approach vs. PDCAM for simplified conditionsPDCAMu p,norm = 1.0Simplified0.90.80.50.250.10.05∆ strength ≈ 5%Both procedures(under similarconditions)give similar results15 of 20

Case 2: Bucket foundationPDCAM: more realistic conditionsAssumptions:• soil with non-linear stressstrainrelationshipHcy100%• pore pressure generation anddissipation in any area anddirectionWe apply the same cyclic load historyNumber of cycles16 of 20

Case 2: Bucket foundationComparisonSimplifiedu p,norm = 1.00.90.80.50.250.10.05PDCAM(simplifiedconditions)PDCAM (morerealistic conditions)Quantify theconservatism17 of 20

Case 2: Bucket foundationPDCAM:(More realisticconditions)Excess porepressures[kPa]10080604020018 of 20

Conclusions• There are no important/significant differences between foundationsfor OWT and other offshore foundations. We may therefore use thesame geotechnical design procedures• UDCAM/PDCAM accounts for the actual design load history andcyclic behaviour of the soil. It can be both stiffer and softer thanstandard (API) p-y curves• The method is validated both against simplified approaches andmodel tests• Requires more knowledge about the cyclic soil behaviour. Needsmore advanced laboratory testing (cyclic tests)• Integrated SSI response accounting for complex soil layering• May give more economical or safe design19 of 20

Thank you for your attention!20 of 20