Drained Clay-Pipe Interface Resistance at Low Normal Stresses and Elevated Temperatures

Offshore pipelines that transport hydrocarbons under high pressure and high temperature are usually thermally insulated to maintain an elevated temperature and prevent any heat loss to the surroundings. However, the temperatures at the outer-wall of the pipes may still be elevated and therefore may potentially affect the interface resistance between the pipeline and the seabed. This study aims at experimentally investigating the drained shear resistance of the soil-pipe interface at elevated temperatures (22–60°C) and low normal stresses typical of field conditions (2.45–6.1kPa). A series of direct shear tests are thus performed using a modified-for purpose direct shear apparatus. Low and high plasticity clays, consolidated from a slurry, were sheared against smooth and rough interfaces to characterize the peak and residual interface shear response under drained conditions. Results indicated that the effect of elevated temperature on the interface resistance is highly complex and dependent on the roughness of the pipe coating, the plasticity of the clay, and the magnitude of the applied normal stress.