Transient behaviour of a suction caisson in sand: axisymmetric - PowerPoint PPT Presentation

Transient behaviour of a suction caisson in sand: axisymmetric numerical modelling B. Cerfontaine, F. Collin and R. Charlier University of Liege, Belgium 26th of May, 2016 B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 0 / 24

Outline Context 1 Description of the case study 2 Results 3 Conclusions and perspectives 4 B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 1 / 24

Context Table of contents Context 1 Description of the case study 2 Results 3 Reaction modes Monotonic simulations Cyclic simulations Conclusions and perspectives 4 B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 2 / 24

Context Motivations 1 EU 2020 objectives (greenhouse gas, renewable energy , energy efficiency) B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 3 / 24

Context Motivations 1 EU 2020 objectives (greenhouse gas, renewable energy , energy efficiency) 2 Basic working of soil-caisson system upon both monotonic and cyclic loading (serviceability) B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 3 / 24

Context Motivations 1 EU 2020 objectives (greenhouse gas, renewable energy , energy efficiency) 2 Basic working of soil-caisson system upon both monotonic and cyclic loading (serviceability) 3 Identifications of components of reaction : first step to the elaboration of a macro-element B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 3 / 24

Context Suction caissons for offshore foundations Offshore wind turbines specificities Houlsby et al. (2005) light structure high overturning moment Suction caissons specificities hollow steel cylinder open towards the bottom extensively used as anchors in the North Sea monopod or tetra/tri-pod Pumping superstructure cheaply and quickly installed, reusable, Decreasing inside pressure Senders (2008) limited extension resistance by suction Water flows B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 4 / 24

Description of the case study Table of contents Context 1 Description of the case study 2 Results 3 Reaction modes Monotonic simulations Cyclic simulations Conclusions and perspectives 4 B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 5 / 24

Description of the case study Geometry Modelling (axisymmetric) Inner Lid interface (top) Sea level Elastic superficial Waves + Wind layer Height (H) Outer Inner interface interface (skirt) (skirt) Seabed Elastic toe Skirt Radius (D/2) Published in Cerfontaine et al. (2016), G´ eotechnique B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 6 / 24

Description of the case study Geometry Modelling (axisymmetric) Loading Sea level Waves + Wind Initial stress Height (H) (soil) Seabed Initial stress (interface) Radius (D/2) Published in Cerfontaine et al. (2016), G´ eotechnique B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 6 / 24

Description of the case study Geometry Size D=7.8m and H=4m Sea level Soil-steel friction coefficient Waves + Wind µ = 0 . 5 Permeability k= 5 · 10 − 12 m 2 Seabed Coefficient of lateral earth pressure at rest K 0 = 1 . 0 Published in Cerfontaine et al. Porosity (2016), G´ eotechnique n= 0 . 36 B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 6 / 24

Description of the case study Prevost model for cohesionless soils - Kinematic hardening After Elgamal (2003) Implementation in LAGAMINE code published in Cerfontaine et al. (2014) NUMGE2014 Proceedings B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 7 / 24

Description of the case study Prevost model for cohesionless soils - Volumetric behaviour Non-associated plastic volumetric behaviour q PT line Dilative 3 · η 2 − ¯ η 2 v = 1 η 2 · ˙ ǫ p ˙ λ Current stress η 2 + ¯ state Trace of current yield surface η Contractive η = q / p ′ p' ˙ λ continuous plastic multiplier η phase transformation ratio, ¯ Ishihara (1975) Very simple (only 1 param.) ⇒ satisfactory to a 1st approx. B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 8 / 24

Description of the case study Cyclic triaxial tests (Lund Sand, Dr= 90%, Ibsen & Jakobsen (1996)) Two distinct behaviours from two initial deviatoric stress invariants 70 70 60 60 PT Line 50 50 40 40 q [kPa] q [kPa] 30 30 20 20 PT Line 10 10 0 0 − 10 − 10 − 20 − 20 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 p’ [kPa] p’ [kPa] Full calibration process published in Cerfontaine (2014), PhD thesis B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 9 / 24

Description of the case study Hydro-mechanically coupled interface element Mechanical behaviour Flow behaviour f>0 |t T | Side 1 Plastic f=0 surface f<0 No contact f wt2 f wl Elastic domain g N Inside µ p' f wt1 N + Penalty method Side 2 Couplings Effective stress Storage Permeability Published in Cerfontaine et al. (2015) Computers and Geotechnics B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 10 / 24

Results Reaction modes Table of contents Context 1 Description of the case study 2 Results 3 Reaction modes Monotonic simulations Cyclic simulations Conclusions and perspectives 4 B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 11 / 24

Results Reaction modes Reaction of the caisson to applied vertical load Δ F tot Δ F tot Δ F tot Δ F tot Δ F top Δ F pw Δ F pw Δ F in Δ F out Δ F in Δ F out Δ F tip Resistance to compressive load Resistance to extension load ∆ F tot ∆ F tot ∆ F in , inner friction ; ∆ F in , inner friction ; ∆ F out , outer friction ; ∆ F out , outer friction ; ∆ F pw , pore water pressure ∆ F pw , pore water pressure ( < 0). ( > 0) ; ∆ F top , top effective stress ; ∆ F tip , tip effective stress. B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 12 / 24

Results Monotonic simulations Table of contents Context 1 Description of the case study 2 Results 3 Reaction modes Monotonic simulations Cyclic simulations Conclusions and perspectives 4 B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 13 / 24

Results Monotonic simulations Monotonic extension simulations (load controlled) Drained Partially drained (8kPa/s) 0 0 ∆ F tot − 0.5 − 0.5 ∆ F in ∆ F out − 1 − 1 ∆ F lid ∆ F [MN] ∆ F [MN] ∆ F tip − 1.5 ∆ F tot − 1.5 ∆ F pw ∆ F in − 2 − 2 ∆ F out ∆ F lid − 2.5 − 2.5 ∆ F tip Upwards Upwards − 3 − 3 − 3 − 2.5 − 2 − 1.5 − 1 − 0.5 0 − 3 − 2.5 − 2 − 1.5 − 1 − 0.5 0 ∆ y [mm] ∆ y [mm] ∆ F in and ∆ F out bounded ∆ F in and ∆ F out bounded ∆ F in < ∆ F out (unloading) ∆ F in < ∆ F out (unloading) ∆ F pw increasing B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 14 / 24

Results Monotonic simulations Pore water pressure generation during extension P load = 55.5kPa Δ p w [kPa] -2.80 -5.70 -8.60 -11.5 -14.4 -17.3 -20.2 -23.1 -26.0 -28.9 -31.8 -34.7 B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 15 / 24

Results Cyclic simulations Table of contents Context 1 Description of the case study 2 Results 3 Reaction modes Monotonic simulations Cyclic simulations Conclusions and perspectives 4 B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 16 / 24

Results Cyclic simulations Pseudo-random and equivalent loadings 1 70 Extreme event 0.8 60 Extreme event 0.6 50 F y /max(|F y |) [ − ] 0.4 Δ P load =45kPa 40 load [kPa] 0.2 P load,av =20kPa 30 0 P 20 − 0.2 10 − 0.4 0 − 0.6 Short Signal − 10 − 0.8 0 0.5 1 1.5 2 0.8 0.85 0.9 0.95 1 Time [h] Time[h] B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 17 / 24

Results Cyclic simulations Pseudo-random and equivalent loadings 1 70 Extreme event 0.8 60 Extreme event 0.6 50 F y /max(|F y |) [ − ] 0.4 Δ P load =45kPa 40 load [kPa] 0.2 P load,av =20kPa 30 0 P 20 − 0.2 10 − 0.4 0 − 0.6 Short Signal − 10 − 0.8 0 0.5 1 1.5 2 0.8 0.85 0.9 0.95 1 Time [h] Time[h] P load Pseudo-Random Δ P 1 Δ P 3 P load,mean Δ P 2 Δ T 1 Time P load Equivalent Δ P 1 Δ P 3 P load,mean Δ P 2 Δ T 1 Time Half-cycle analysis B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 17 / 24

Results Cyclic simulations Pseudo-random and equivalent loadings 1 70 Extreme event 0.8 60 Extreme event 0.6 50 F y /max(|F y |) [ − ] 0.4 Δ P load =45kPa 40 load [kPa] 0.2 P load,av =20kPa 30 0 P 20 − 0.2 10 − 0.4 0 − 0.6 Short Signal − 10 − 0.8 0 0.5 1 1.5 2 0.8 0.85 0.9 0.95 1 Time [h] Time[h] P load Pseudo-Random Δ P 1 Δ P 3 P load,mean Δ P 2 Batch 1 Batch 2 Batch 3 Batch 4 Δ T 1 Nb. cycles [-] 50 28 4 1 Time T [s] 4.6 11 11.6 11.1 P load Equivalent ∆ P [kPa] 4.5 13.5 22.5 40.5 Δ P 1 Δ P 3 P load,mean Δ P 2 Δ T 1 Time Half-cycle analysis B. Cerfontaine, F. Collin and R. Charlier RUGC2016 26/05/16 17 / 24