Input of fully 3D FE soil-structure modelling to the operational analysis of jack-up structures

Jack-ups are mobile structures widely employed in the offshore industry as drilling rigs or installation/maintenance vessels (e.g. for offshore wind farms). To assure safety at each location, site-specific assessment is required to predict the performance of the unit during installation and operations. The response of jack-ups to environmental loads is highly affected by the interaction between all footings (spudcans) and the underlying soil, an interaction still challenging to describe under general 3D loading. This work emphasises the potential of 3D continuum simulations to capture non-linear soil-structural interaction in jack-up units. An integrated jack-up–spudcans-soil 3D finite element (FE) model is set up by including strain-hardening soil plasticity and geometrical non-linearity (P−Δ effects). After preliminary calibration of soil parameters, the FE model is successfully validated against literature results, namely obtained through (i) small-scale centrifuge experiments and (ii) numerical simulations based on macroelement foundation modelling. The validated FE model is then used to inspect several implications of soil modelling assumptions, as well as the response of the jack-up to relevant 3D loading combinations. The results presented support 3D continuum modelling as a suitable approach to analyse spudcan fixity and, overall, the operational performance of jack-ups. Despite higher conceptual/computational difficulties, fully 3D simulations can valuably complement the insight from (rare) integrated physical modelling, and contribute to the improvement of soil-spudcan macroelement models.

[1]  Mark Cassidy,et al.  A plasticity model for the behaviour of footings on sand under combined loading , 2002 .

[2]  Mark Cassidy,et al.  Assessing appropriate stiffness levels for spudcan foundations on dense sand , 2010 .

[3]  A. Elgamal,et al.  Modeling of cyclic mobility in saturated cohesionless soils , 2003 .

[4]  Michael C. Georgiadis,et al.  DISPLACEMENTS OF FOOTINGS ON SAND UNDER ECCENTRIC AND INCLINED LOADS , 1988 .

[5]  Guido Gottardi,et al.  Plastic response of circular footings on sand under general planar loading , 1999 .

[6]  Christophe Gaudin,et al.  Centrifuge tests of shallow footing behaviour on sand under combined vertical-torsional loading , 2007 .

[7]  Mark Cassidy,et al.  Numerical simulation of pushover tests on a model jack-up platform on clay , 2011 .

[8]  Mark Cassidy,et al.  Investigating six-degree-of-freedom loading of shallow foundations on sand , 2006 .

[9]  Mike Hoyle,et al.  Jack-Up Assessment - Past, Present And ISO , 2006 .

[10]  M. Hoyle,et al.  Jack-up Response Measurements and the Underprediction of Spud-Can Fixity By SNAME 5-5A , 2000 .

[11]  H. Saunders,et al.  Finite element procedures in engineering analysis , 1982 .

[12]  W. G. Versteijlen,et al.  3D FE dynamic modelling of offshore wind turbines in sand: natural frequency evolution in the pre– to after-storm transition , 2018 .

[13]  Foundation Modeling and Assessment in the New ISO Standard 19905-1 , 2012 .

[14]  G.J.M. Schotman,et al.  Aspects of the stability of jack-up spud-can foundations , 1989 .

[15]  Okky Ahmad Purwana,et al.  Comparison of ISO 19905-1 Framework and a Plasticity-based Spudcan Model for Jackup Foundation Assessments , 2012 .

[16]  Guy T. Houlsby,et al.  A model for nonlinear hysteretic and ratcheting behaviour , 2017 .

[17]  Mark Cassidy,et al.  Advances in the three-dimensional fluid–structure–soil interaction analysis of offshore jack-up structures , 2006 .

[18]  Guy T. Houlsby,et al.  Combined loading of spudcan foundations on clay: numerical modelling , 2001 .

[19]  N. Cheng.  Force-resultant models for shallow foundation systems and their implementation in the analysis of soil-structure interactions , 2015 .

[20]  Richard E. Goodman,et al.  CLOSURE ON A MODEL FOR THE MECHANICS OF JOINTED ROCK , 1968 .

[21]  Mark Cassidy,et al.  Three-dimensional numerical analysis of centrifuge experiments on a model jack-up drilling rig on sand , 2009 .

[22]  Christophe Gaudin,et al.  Physical modelling of the push-over capacity of a jack-up structure on sand in a geotechnical centrifuge , 2009 .

[23]  Mark Cassidy,et al.  Evaluation of long-term extreme response statistics of jack-up platforms , 2002 .

[24]  Chun Fai Leung,et al.  Improved Guidelines for the Prediction of Geotechnical Performance of Spudcan Foundations During Installation and Removal of Jack-up Units , 2009 .

[25]  A. N. Schofield,et al.  Centrifuge modelling of jackups and spudcans on drained and partially drained silica sand , 1995 .

[26]  A. N. Schofield,et al.  NUMERICAL MODELLING OF THREE-LEG JACKUP BEHAVIOUR SUBJECT TO HORIZONTAL LOAD , 1997 .

[27]  Mark Cassidy,et al.  Experimental investigation of the system behaviour of a model three-legged jack-up on clay , 2008 .

[28]  I. Herle,et al.  Hypoplastic model for cohesionless soils with elastic strain range , 1997 .

[29]  G.J.M. Schotman.  The Effects of Displacements on the Stability of Jackup Spud-Can Foundations , 1989 .

[30]  Gerhard A. Holzapfel,et al.  Nonlinear Solid Mechanics: A Continuum Approach for Engineering Science , 2000 .

[31]  Tim Pucker,et al.  CPT based prediction of foundation penetration in siliceous sand , 2013 .

[32]  R. Nova,et al.  Settlements of shallow foundations on sand , 1991 .

[33]  Guy T. Houlsby,et al.  Interactions in offshore foundation design , 2016 .

[34]  Majid T. Manzari,et al.  SIMPLE PLASTICITY SAND MODEL ACCOUNTING FOR FABRIC CHANGE EFFECTS , 2004 .

[35]  Hans Petter Jostad,et al.  Finite Element Analyses Applied in Design of Foundations and Anchors for Offshore Structures , 2011 .

[36]  Tor Inge Tjelta,et al.  Skirted spud-cans — Extending operational depth and improving performance , 1996 .

[37]  Daniel Karunakaran,et al.  Full-scale measurements from a large deepwater jack-up platform , 1999 .

[38]  Mark Cassidy,et al.  The behaviour of spudcan footings on clay subjected to combined cyclic loading , 2006 .

[39]  F. Pisanò,et al.  Enhanced plasticity modelling of high-cyclic ratcheting and pore pressure accumulation in sands , 2018 .

[40]  Mark Cassidy,et al.  Development of a model jack-up unit for the study of soil-structure interaction on clay , 2005 .

[41]  A. E. Groen.  Three-Dimensional Elasto-Plastic Analysis of Soils , 1997 .

[42]  Mark Cassidy,et al.  Jack-up push-over analyses featuring a new force resultant model for spudcans in soft clay , 2014 .

[43]  Mark Cassidy,et al.  Analysis of jack-up units using a Constrained NewWave methodology , 2001 .

[44]  Gholamreza Mesri,et al.  Soil-foundation modelling in laterally loaded historical towers , 2014 .

[45]  Claudio di Prisco,et al.  Seismic response of rigid shallow footings , 2011 .

[46]  Mark Cassidy,et al.  Development and application of force resultant models describing jack-up foundation behaviour , 2004 .

[47]  Diana Salciarini,et al.  A hypoplastic macroelement model for shallow foundations under monotonic and cyclic loads , 2009 .

[48]  Mark Randolph,et al.  Offshore Geotechnical Engineering , 2011 .

[49]  Federico Pisanò,et al.  Transient response of offshore wind turbines on monopiles in sand: role of cyclic hydro–mechanical soil behaviour , 2017 .

[50]  Mark Cassidy,et al.  A plasticity model for spudcan foundations in soft clay , 2014 .

[51]  A. N. Schofield,et al.  Drum centrifuge study of three-leg jackup models on clay , 1998 .

[52]  D. Borst,et al.  Fundamental issues in finite element analyses of localization of deformation , 1993 .

[53]  Dong Wang,et al.  Numerical modelling of the effects of consolidation on jack-up spudcan penetration , 2016 .

[54]  P. W. Rowe.  The stress-dilatancy relation for static equilibrium of an assembly of particles in contact , 1962, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.