Abstract: The effect of three influential factors including the pause period, the loading rate and the undrained shear strength of soft clay on the axial friction property is investigated using the laboratory model test, when the relative axial displacement of the full-scaled PE-coated pipe and the soft clay take place. The research revealed that there are two forms of force-displacement curves of pipe-clay axial interaction: hardening type and softening type. The peak resistance mobilization distance ranges of 0.005D to 0.02D (D: the diameter of the pipe) for softening type while appears in the last stage of the loading process for hardening type. The peak measured friction coefficients ranged from 0.12 to 0.23 are less than the API recommended values. The peak fiction coefficients are positively related to the loading rates; but the loading rates have no significant effect on the forms of force-displacement curves. The fiction coefficients of clay with high shear strength are lower than the fiction coefficients of clay with low shear strength within the scope of common undrained shear strengths. The conclusion provides references for determining the friction coefficient of axial interaction between buried marine pipeline and clay.

Key words: buried pipeline, marine soft clay, axial interaction, model test, pipeline-soil friction coefficient