Theoretical modelling of a suction caisson foundation using hyperplasticity theory Lam Nguyen-Sy and Guy Houlsby

1. Oxford University Civil Engineering – ISFOG, Perth, September 2005 t v = V/V0 1.0 t0 Initial fraction = 0.8 Theoretical modelling of a suction caisson foundation using hyperplasticity theoryLam Nguyen-Sy and Guy Houlsby MOTIVATION: the purpose is to define a complete theoretical model which describes the behaviour of a caisson foundation under general loading. The model, which is called “ISIS”, can be incorporated into the numerical analysis of a structure such as a wind-turbine The model is expressed in terms of “force resultants” on the foundation (and the corresponding displacements) rather than in terms of details of stress and strain within the soil HYPERPLASTICITY is used as the framework for the model. In this approach the response is defined by specifying two scalar functions, for instance the Gibbs free energy and the yield function. The model uses “continuous hyperplasticity” which allows many yield surfaces to be specified. Monopod caisson foundation Tripod or tetrapod caisson foundation EXAMPLE ANALYSES show comparisons between laboratory tests and the “ISIS” model The Gibbs free energy defines various aspects of behaviour: The analysis can deal with special features such as suction-installed caissons Elasticity Plastic strains Strain hardening Cyclic response with changing stiffness and hysteresis can be modelled The other important expression is the yield function: Vertical movements during cyclic moment loading are predicted The model is implemented in numerical calculations using a rate-dependent formulation in the time domain: This research has been supported by the DTI, EPSRC, Vietnamese Government, SLP, Fugro, Garrad Hassan, GE Energy, Shell and Vestas See also www-civil.eng.ox.ac.uk