Pipe-Soil Interaction In Soft Clays

Flowlines and pipelines in Offshore area are generally laid on the surface of the sea-bed under their own weight without burial in a trench. These pipelines may experience lateral buckling and axial walking due to the expansion caused by the operating temperature and pressure. Analysis of pipe-soil interaction is required to assess, control and limit buckling. This analysis should include Geotechnical data collection and interpretation and evaluation of the lateral and axial resistance that a pipeline develops to resist the expansion forces. This paper consists of three parts. The first part discusses the importance of site specific geotechnical characterisation in order to identify strength and deformation parameters of the very shallow layers. Reference is made to recent projects in deep offshore West Africa. The second part is a summary of the results of pipe-soil interaction experiments conducted on reconsolidated soft clay recovered from deep offshore West Africa. These laboratory experiments included measurements of axial and lateral resistances of pipe sections partially embedded in a tank of clay. Extensive instrumentation was used to measure forces and displacements of the tested pipe sections. In the third part simplified methods and practical calculations are proposed to evaluate the axial and lateral pipeline resistance mobilisation curves. These calculations are based on the general soil mechanics rules and calibrated using the results of the pipe-soil interaction experiments presented in the second part. Parameters such as pipe over-penetration and the development of soil berms during lateral movement will be briefly presented as they may highly influence the lateral soil resistance