Residual Shear Strength for Interfaces between Pipelines and Clays at Low Effective Normal Stresses

Abstract

The residual shear strength mobilized between pipelines and supporting soils at low effective normal stresses is needed for designing stable pipelines in offshore environments. A tilt table device is used to study the effect that effective normal stress, type of pipeline coating, composition of soil, stress history, and rate of loading have on the drained residual shear strength mobilized at the interface between a variety of clays and polymeric pipe coatings. The drained residual friction angles for both the interfaces and the clays decrease substantially as the effective normal stress increases. Empirical correlations published for predicting the residual strength of clays cannot be readily extrapolated to the pipeline problem because the correlations do not cover the relatively small effective normal stresses acting on pipelines. Residual shear strengths for the interfaces range from 60 to 90% of the residual shear strength for the clay. The residual shear strength for the interface depends both on the composition of the clay and the type of pipeline coating.