Drained Bearing Capacity of Shallowly Embedded Pipelines

This study establishes the drained bearing capacity of pipelines embedded up to one diameter into the seabed subject to combined vertical-horizontal loading. Nonassociated flow finite-element analyses are used to calculate the peak breakout resistance in a frictional Mohr-Coulomb seabed. Critical state friction angles and dilation angles ranging from 25° to 45° and from 0° to 25°, respectively, are considered. Analytical expressions are fitted to the results as a function of embedment depth and soil properties, and compare well with experimental measurements from previous studies. The horizontal bearing capacity at small vertical loads is also predicted well via upper-bound limit analysis using the Davis reduced friction angle that accounts for the peak friction and dilation angles. The analytical relationships presented in this study provide simple predictive tools for estimating the bearing capacity of pipelines on free-drained sandy seabeds. These fill a void in knowledge for pipeline stability and buckling design by providing general relationships between drained strength properties and pipeline bearing capacity. The insight gained through the good comparison with limit analysis techniques also gives confidence in the use of simple numerical techniques to predict the bearing capacity of pipelines for more wide-ranging (i.e., nonflat) seabed topography.