Axial shear friction of polypropylene pipes against granular beds

The axial pipe-soil shear resistance is an important feature in various subsea pipeline designs such as axial walking, buckling and end expansions. In deeper water, subsea pipelines are generally laid simply on the seabed and polymer coatings are widely used to protect pipelines from abrasion and erosion. There exists little guidance on the mobilised frictional forces between pipeline coatings and the seabed. A new device has been developed at the University of Bristol for the purpose of evaluating pipeline interface friction, and it enables the testing of large pipe sections (outer diameter up to about 0.4m) and up to cobble sized granular beds. A series of axial pipe-soil shear tests have been conducted between a segment of polypropylene pipe and a variety of underlying granular beds of different characteristics under normal stresses levels lower than 20kPa, typical of as-laid subsea pipelines. Results from the experiments have been used to determine a relationship between axial interface friction and granular soil properties, considerably expanding information available in the literature and reducing uncertainties in subsea pipeline design.