Pipe soil interaction is an aspect which is increasingly being addressed in the design of deepwater HPHT pipelines and considerable progress has been achieved in the characterization of models to be used in finite element analysis procedures. However, because of the complexity involved and the limitations of the available software to deal with such numerically challenging models, the benefits from incorporating such models remain under exploited as most analysis procedures still rely on simplified Coulomb friction models. This paper first presents an overview of pipe-soil interaction models used in recent deepwater West Africa developments. It addresses the procedures for calculating the embedment and the resulting axial and lateral frictional resistances for both monotonic and cyclic conditions. The paper examines the influence of these parameters for the extreme and cyclic conditions for lateral buckling, pipe walking and interaction between lateral buckling and pipe walking. It is shown that while detailed pipe soil interaction models can lead to optimization in the analysis results, there is a degree of uncertainty in the applicability of these models and considerations should be given to consolidated procedures that allow optimization of the design solutions but at the same time accommodate any design uncertainty.
For a number of deepwater projects executed in recent years, the approach for formulating the pipe soil interaction follows a common procedure for the pipe embedment and the soil frictional resistance. The embedment, which defines the initial condition of the pipe following installation, is fundamental to defining the axial and lateral friction. The embedment is a function of a number or parameters including the soil conditions, the effective weight and the effects of installation. The best estimate embedment is usually calculated using nominal values for these parameters and calibration factors are used to define lower and upper bound values.
