TABLE OF CONTENTS An interaction model of the contact between the pipeline and the seabed are often referred to as a pipe/soil interaction model. The pipe/soil interaction model consists of seabed stiffness and equivalent friction definition to represent the soil resistance to movement of the pipe. The equivalent friction is mainly based on coulumb friction (sand), cohesion (clay) or a combination of the two (silty-, sand- clays), the soil density and the contact pressure between the soil and pipe. It is therefore important to predict the soil contact pressure, equivalent friction and soil stiffness accurately.
In a finite element model a non-linear pressure/penetration relationship may be used. The penetration of a statically loaded pipe into soil can be calculated as a function of pipe diameter, vertical contact pressure, soil strength parameters (undrained shear strength for clay and internal friction angle for friction materials such as sands) and submerged soil density. This penetration is to some extent complicated by the circular form of the pipeline, which leads to a combined effect of friction and bearing capacity resisting soil penetration.
In order to construct the pressure/penetration relationship mentioned above, an approach based on different methods for calculating the seabed penetration as a function of the static ground pressure has been used. Two such methods for clayey soils are the Verley and Lund (1995) method, and the buoyancy method (Haland, 1997). It is also clear that this is an approximation, since cyclic soil effects are ignored. In the following...
