A novel pipe-segment shear test apparatus: polypropylene pipe behaviour over sand beds versus element interface tests

This study describes a novel laboratory test apparatus for investigating the axial interaction between pipeline and soil. Contrary to the majority of existing pipe-soil shear rigs, the proposed apparatus applies a relative pipe-soil shear displacement through driving a soil box below an axially restrained pipe segment, which is instrumented to measure the pipe settlement and the axial resistance at the pipe-soil contact surface. Through axial shear tests of polypropylene pipe segment on sand, this study explores the effect of vertical loads, soil types, and densities on the resulting axial resistance and estimates the interface stress evolution. The coefficients of axial resistance obtained from large-scale pipe-soil shear tests are compared to those obtained via planar element interface shear tests with consideration of the wedging effect. Their consistency suggests that under the low stress levels investigated in this study, the effect of both pipeline curvature and settlement on the resultant data are minor. The agreement provides validation for the novel apparatus to generate high-quality data under controlled conditions for future studies. The findings of this study will also potentially help reduce the uncertainties around subsea pipeline design when linking the interface shear behaviour at element scale to large-scale pipe-soil interaction.