Effect of Soil Composition, Interface Roughness, and Drainage Response on Shear Strength During Low Normal Stress Interface Shear Box Testing

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4. Effect of Soil Composition, Interface Roughness, and Drainage Response on Shear Strength During Low Normal Stress Interface Shear Box Testing

Subsea pipelines are a crucial component of offshore infrastructure for the development of oil and gas fields. These pipelines experience thermally induced axial and lateral displacements due to temperature changes during operation. The frictional resistance to these displacements can be drained or undrained, depending on the rate of pipe displacement and soil drainage characteristics, and is also affected by normal stress levels and pipe surface coating characteristics. This paper examines the effect of soil composition, shearing rate, and interface roughness on the transition from undrained to drained residual interface shear stress during cyclic interface shear box (ISB) tests. The cyclic ISB testing comprised continuous cyclic shearing at a fast shearing rate of 0.1 mm/s to achieve undrained residual conditions. Cyclic shearing was continued through the drainage transition until steady state conditions were achieved, followed by a pair of confirmatory cycles at a slow shearing rate of 0.001 mm/s. Tests were conducted on smooth, intermediate, and rough interface plates using three different normally-consolidated soil specimens with varying fines and sand content. The study provides insights into the drainage behavior of transitional or mixed soil types often encountered in intermediate and shallow water depths gas export pipelines, and its effect on residual interface strength as it relates to the governing load transfer mechanisms. The paper builds upon a large body of work amassed over the past two decades on low normal stress interface shear testing and provides further guidance on the conduct and interpretation of these tests for development of pipe-soil interaction parameters used in pipeline design.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

2 - Site characterization, in-situ and laboratory testing, measurement