This paper presents results from model tests designed to measure the drained residual axial resistance between a flowline and a marine clay. Tests were conducted with different flowline weights, soil strengths, and axial loading conditions in order to explore the magnitude of and the path to mobilizing the drained residual axial resistance. Drained conditions at the interface between the 108-mm diameter pipe and marine clay were mobilized at axial loading speeds of about 0.0005 mm/s. Once the drained residual condition is reached, the loading speed can be increased at least 100 times in the same direction with no change in the axial resistance. The drained residual condition at the interface between the pipe and the marine clay can also be mobilized by performing numerous cycles of loading at axial loading speeds greater than those needed for drained conditions. The axial load test results are similar to tilt table results with both indicating a significant reduction in drained residual resistance with increasing normal stress. However, the axial resistance for the pipes can be affected by continued consolidation of the soil at the pipe interface after placement, which was apparently on the order of 50 to 100 days after placement, and by a change in the effective contact area supporting the weight of the pipe with time and/or previous shearing cycles.
Ahmed M. Hussien, R. B. Gilbert, Y. Huang, C. Sung, J. Han, L. Melo Monteiro, J. Chen, K. Ouyang and M. Luo
Keywords: offshore oil and gas, flowline, pipeline, pipe-soil interaction, soil-structure interaction
Publisher: DFI