An effective stress framework for the variation in penetration resistance due to episodes of remoulding and reconsolidation

Steel catenary risers (SCRs) are used to transport hydrocarbon products between offshore floating platforms and the seabed. Like many offshore structures, SCRs are subjected to gross cyclic movements during operation, which remould the seabed soil. The fatigue life of these structures is highly sensitive to the stiffness and strength of the seabed response. Accurate modelling of this behaviour requires a framework that can capture the changes in soil strength and stiffness that occur throughout the design life, accounting for remoulding during extreme events, and reconsolidation during the intervening periods. This paper describes such a framework, which is couched in effective stress terms. Soil softening during remoulding is predominantly associated with excess pore pressure generation, and the subsequent regain in strength is linked to the dissipation of excess pore pressure. The framework can describe the variation of resistance on a cylinder (i.e. a pipe) during any sequence of vertical cyclic motion...

[1]  David White,et al.  Analysis of Soil Strength Degradation during Episodes of Cyclic Loading, Illustrated by the T-Bar Penetration Test , 2010 .

[2]  D. M. Potts,et al.  The behaviour of Drammen Clay under cyclic loading , 1978 .

[3]  Mark Randolph,et al.  Non-Linear Hysteretic Seabed Model for Catenary Pipeline Contact , 2009 .

[4]  M. Randolph,et al.  The limiting pressure on a circular pile loaded laterally in cohesive soil , 1984 .

[5]  K. Andersen.  Bearing capacity under cyclic loading ― offshore, along the coast, and on land. The 21st Bjerrum Lecture presented in Oslo, 23 November 2007 , 2009 .

[6]  C. P. Wroth,et al.  The interpretation of in situ soil tests , 1984 .

[7]  David White,et al.  A simple model for the effect on soil strength of episodes of remoulding and reconsolidation , 2010 .

[8]  C. Bridge,et al.  Effects of seabed interaction on steel catenary risers , 2005 .

[9]  Chris M. Martin,et al.  Upper-bound analysis of lateral pile capacity in cohesive soil , 2006 .

[10]  Malcolm D. Bolton,et al.  Pipe-Soil Interaction With Flowlines During Lateral Buckling and Pipeline Walking - The SAFEBUCK JIP , 2008 .

[11]  Alan G. Young,et al.  Soil Response and Stiffness Laboratory Measurements of SCR Pipe/Soil Interaction , 2008 .

[12]  Mark Randolph,et al.  Catalogue of scaling laws and similitude questions in geotechnical centrifuge modelling , 2007 .

[13]  E. Clukey,et al.  Steel Catenary Riser Touchdown Point Vertical Interaction Models , 2004 .

[14]  David White,et al.  Consolidation around partially embedded seabed pipelines , 2011 .

[15]  H. A. M. Van Eekelen,et al.  SINGLE PARAMETER MODELS FOR PROGRESSIVE WEAKENING OF SOILS BY CYCLIC LOADING , 1977 .

[16]  L. Bjerrum,et al.  Geotechnical problems involved in foundations of structures in the North Sea , 1973 .

[17]  Andrew Palmer,et al.  Geotechnical evidence of ice scour as a guide to pipeline burial depth , 1997 .

[18]  David White,et al.  Effect of Remodling and Reconsolidation on the Touchdown Stiffness of a Steel Catenary Riser: Guidance from Centrifuge Modelling , 2009 .