Predicting the ultimate bearing capacity of a deep-sea pipeline on the soft clayey seabed is crucial for on-bottom stability and global buckling analyses. Based on slip-line field theory, an analytical solution is derived for the undrained bearing capacity of an obliquely-loaded pipeline on a clayey seabed obeying Tresca criterion. For a wished-in-place pipeline, the failure mechanisms and the corresponding pipe-soil interface conditions are proposed for the vertical and the lateral instability mode, respectively. Based on the derived slip-line field solution, a series of failure envelopes are established for various pipe-soil interface conditions. The analytical solution matches well with the previous numerical and theoretical results. Parametric study indicates that the embedment-to-diameter ratio and the loading angle are the key parameters for the bearing capacity of an obliquely-loaded pipeline.
Soft clayey sediments are widely distributed in the deep waters of South China Sea (see Liu et al., 2021). The deep-sea pipelines are generally laid directly on the seabed, where the pipelines may penetrate partially or even completely into the soil during their service period (DNV GL, 2017). Under the action of ocean currents, a partially-embedded pipeline would suffer an oblique hydrodynamic loading including the drag (horizontal) and the lift (vertical) forces. While the deep-sea pipeline transports oil and gas with high temperature and high pressure, an axial compressive force could be induced along the pipeline (Taylor and Gan, 1986). Under the external (hydrodynamic forces) or/and the internal (axial compressive force due to the rise of temperature and pressure) loads, the pipeline may break away from its original location while losing on-bottom stability (Gao et al., 2007) and even buckle along the seabed surface (Bruton et al., 2006). As such, a reliable assessment of the ultimate bearing capacity of an obliquely-loaded pipeline on the clayey seabed is necessary for predicting the instability of deep-sea pipelines (Fredsøe, 2016; Gao, 2017).
