Geotechnical challenges for the design of large diameter monopiles Fabian Kirsch 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 1 GuD‘s Range of Engineering Capabilities and Professional Services Geotechnical and foundation engineering Soil dynamics and earthquake engineering Protection against structure-borne vibrations 9 80 8 70 71 68 60 55 Umsatz in Mio. Euro 50 7 61 Angestellte 48 48 49 46 47 43 41 40 40 42 40 5 4 34 30 3 20 23 Berlin office 2 17 10 0 On-site measurement technology 6 52 52 46 46 Site management Quality Management Structural Engineering Tunnelling 1 1 1 1 2 2 2 3 3 4 4 6 8 0 Geoenvironmental engineering 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 2 GuD locations Hamburg GuD Offices Berlin GuD Representatives Potsdam Köln Leipzig Mainz 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 3 GuD involvements in North- and Baltic Sea 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 4 Monopile Foundation Predominant lateral cyclic loading 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 5 Embedment functions: non-linear “p-y-curves” Advantages: • long experience for “normal” size piles • easy to use and implement in structural models • correlated to standard geotechnical parameters Shortcomings: • uncoupled Winkler springs • adjusted for approx. D=1m << 6m…10m • cyclic effects incl. PWP development not appropriately included 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 6 DONG, 2012 Measured frequency Design soil stiffness needs to increase 2-3 times Design frequency Reference: Kallehave D, LeBlanc Thilsted C and Liingaard M (2012) Modification of the API p-y Formulation of Initial Stiffness of Sand. Proceedings of the 7th International Conference on Offshore Site Investigation and Geotechnics. Society for Underwater Technology 2012. 02.07.2014 | 4th Int. Conf. Offshore Foundations 7 | IQPC - Bremen 7 F m H F m 02.07.2014 | 4th Int. Conf. Offshore Foundations Pore Water Pressure Accumulation (Liquefaction?) | IQPC - Bremen 8 Tasan, 2011 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 9 Densification of a dense sand Scaled Model Tests BAM, 2011 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 10 Predominant lateral cyclic loading Modification p-y curves 1. Adjustment for large diameter 2. Adjustment for small strain dynamic loading 3. Adjustement for layered soil Cyclic effects -Grain redistribution -Densification / Loosening -Stiffening / Softening -Accumulation of deformations -Pore pressure accumulation -Liquefaction / Cyclic mobility / loss of stability 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 11 • OWA project lead by DONG with numerous partners • Academic Work Group (ICL, Uni Oxford, Uni Dublin) to develop enhanced models for lateral pile behaviour 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 12 Modified p-y curves 1. Adjustment of the p-y-curves for large diameter by reduction of shear strength 8000 7000 'red ' f ( D 2, 0) 1 6000 f 0,3...0,5 p [kN/m] 5000 4000 3000 2000 API Standard - Zyklisch 1000 API mit Anpassung für Durchmesser (reduzierte Steifigkeit) - Zyklisch 0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 y [m] 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 13 2. Adjustment of the p-y-curves for small strains under dynamic loading (EA „Baugrunddynamik“) (EA „Baugrunddynamik“) 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 14 2. Adjustment of the p-y-curves for small strains under dynamic loading 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 15 2. Adjustment of the p-y-curves for small strains under dynamic loading Esd 10 -0,42 * log(0,0006* Es ) Es Esd k Es 8000 7000 6000 p [kN/m] 5000 2 4000 3000 2000 API Standard API mit Anpassung für Durchmesser (reduzierte Steifigkeit) 1000 API mit Anpassung für Durchmesser und Dynamik 0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 y [m] 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 16 3. Adjustment of the p-y-curves for layered soil (Georgiadis, 1983) 8000 7000 6000 p [kN/m] 5000 3 4000 3000 2000 API Standard API mit Anpassung für Durchmesser (reduzierte Steifigkeit) 1000 API mit Anpassung für Durchmesser und Dynamik API mit Anpassung für Durchmesser und Dynamik unter Berücksichtigung der äquivalenten Tiefe 0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 y [m] 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 17 Summing up the effects for modified p-y-curves: 8000 7000 6000 p [kN/m] 5000 4000 3000 API Standard API mit Anpassung für Durchmesser (reduzierte Steifigkeit) 2000 API mit Anpassung für Dynamik (Esd/Es) API mit Anpassung für Durchmesser und Dynamik 1000 Angesetzt: API mit Anpassung für Durchmesser und Dynamik unter Berücksichtigung der äquivalenten Tiefe (Georgiadis, 1983) 0 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 y [m] 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 18 Cyclic effects Necessity of element testing in comparable late project phases in order to calibrate soil behaviour fittet to models used 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 19 Cyclic effects [kPa] Zyklische Scherung Wechsellast drainiert ±0,5% 0,0 e[-] [kPa] g[%] Stiffness increase 02.07.2014 | 4th Int. Conf. Offshore Foundations Compaction N[-] | IQPC - Bremen 20 Cyclic effects [kPa] Zyklische Scherung Schwelllast drainiert 13 kPa, 0=13 kPa t e[-] [%] Log? Accumulation Log? of strain N[-] N[-] 02.07.2014 | 4th Int. Conf. Offshore Foundations Compaction | IQPC - Bremen 21 Cyclic effects Glasenapp, TU Berlin (2013) Influence of average stress 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 22 Cyclic effects Phänomene - Sturm vs. Lebensdauer Glasenapp, TU Berlin (2013) Influence of large preshearing 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 23 Cyclic effects Phänomene – Zulässigkeit von Klassierungen Glasenapp, TU Berlin (2013) Influence of order of loading 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 24 Cyclic effects [kPa] [kPa] Zyklische Scherung Wechsellast undrainiert Cyclic mobility u [kPa] s[kPa] PWP accumulation Softening N[-] N[-] 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 25 u [kPa] Cyclic effects 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 26 Cyclic effects 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 27 Cyclic effects These calibrated functions can be implemented in material models for continuum models 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 28 Cyclic effects Modelling Two effects need to be considered PWP -Accumulation Consolidation - Drainage 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 29 Cyclic effects Modelling 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 30 Cyclic effects Modelling 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 31 Cyclic effects Modelling Two effects need to be considered PWP -Accumulation Consolidation - Drainage 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 32 Cyclic effects Clean Sand vs. Cohesive Material 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 33 Cyclic effects Analysis of PWP-accumulation Repräsentative Monopile Location Start Aufbereitung der Lasten aus BSH-Sturm Interaktionsdiagramme aus Elementversuchen Akkumulation in Plateau 1 Akkumulation in Plateau 2 Akkumulation in Plateau 3 Materialparameter unter Berücksichtigung der Akkumulation von Porenwasserdruck und Schubverzerrungen Standsicherheit unter ULS-Last Akkumulierte Verformungen zulässig? nein ja 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 34 Cyclic effects Analysis of PWP-accumulation Repräsentative Monopile Location -Water depth 31.60m -Pile embedment 37.5m -Cohesive layers of little permeability 11m < z < 18m 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 35 Cyclic effects Analysis of PWP-accumulation Aufbereitung der Lasten aus BSH-Sturm Equivalent loading (acc. to Seed) for each plateau : 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 36 Cyclic effects Analysis of PWP-accumulation Interaktionsdiagramme aus Elementversuchen 02.07.2014 | Porewaterpressure 4th Int. Conf. Offshore Foundations | IQPC - Bremen 37 Cyclic effects Analysis of PWP-accumulation Interaktionsdiagramme aus Elementversuchen 02.07.2014 | Strain accumulation 4th Int. Conf. Offshore Foundations | IQPC - Bremen 38 Cyclic effects Analysis of PWP-accumulation Akkumulation in Plateau i 02.07.2014 | FE-Model 4th Int. Conf. Offshore Foundations | IQPC - Bremen 39 Cyclic effects Analysis of PWP-accumulation Akkumulation in Plateau i FE-Model Pfahlkopfbereich 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 40 Cyclic effects Analysis of PWP-accumulation Akkumulation in Plateau i 02.07.2014 | Clusterweise applizierter Porenwasserdruck (zu Beginn von Plateau 1) 4th Int. Conf. Offshore Foundations | IQPC - Bremen 41 Cyclic effects Analysis of PWP-accumulation Akkumulation in Plateau i 02.07.2014 | PWP at end of Plateau 1 (after Consolidation) 4th Int. Conf. Offshore Foundations | IQPC - Bremen 42 Cyclic effects Analysis of PWP-accumulation Akkumulation in Plateau i 02.07.2014 | PWP at end of Plateau 2 (after Consolidation) 4th Int. Conf. Offshore Foundations | IQPC - Bremen 43 Cyclic effects Analysis of PWP-accumulation Akkumulation in Plateau i 02.07.2014 | PWP at end of Plateau 3 (after Consolidation) 4th Int. Conf. Offshore Foundations | IQPC - Bremen 44 Cyclic effects Analysis of PWP-accumulation Materialparameter unter Berücksichtigung der Akkumulation von Porenwasserdruck und Schubverzerrungen SOFTENING 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 45 Cyclic effects Analysis of PWP-accumulation Materialparameter unter Berücksichtigung der Akkumulation von Porenwasserdruck und Schubverzerrungen STRENGTH REDUCTION 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 46 Cyclic effects Analysis of PWP-accumulation Akkumulierte Verformungen Akkumulierte Pfahlkopfverdrehungen während des BSH-Sturms (Plateau 1 bis 3) 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 47 Cyclic effects Analysis of PWP-accumulation Overall safety (Fellenius rule) reduced only by a small percentage 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 48 Summary: • To date monopiles incorporate design challenges for stiffness an deformation assessment • Adjustments of p-y-Model is necessary in order to get realistic response of large diameter monopiles under cyclic lateral loading • Pore water pressure build up and its effect on stability needs to be evaluated • Failure of soil support even incl. PWP accumulation is not design driving • Further measurement data needed to verify proposed methods • Neccessity of instrumented monopile foundations 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 49 02.07.2014 | 4th Int. Conf. Offshore Foundations | IQPC - Bremen 50
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