Ultimate bearing capacity of a pipeline on clayey soils: Slip-line field solution and FEM simulation

The ultimate bearing capacity of a cylindrical foundation (e.g. a submarine pipeline, circular mooring lines) on clayey soils is analyzed analytically and numerically by employing the slip-line field theory and the plane-strain finite element method respectively. A slip-line field solution is presented, taking into account of circular configuration of the pipe, the pipe embedment, and the pipe-soil interfacial cohesion. The derived bearing capacity factors for a smooth rigid pipe may limit to those for the conventional rectangle-shaped strip footing while the pipe embedment is approaching zero. A plane-strain finite element model is further proposed to simulate the quasi-static process of the pipeline penetrating into the clay soil, in which the contact-pair algorithm and adaptive meshing technique are employed, and the Drucker-Prager constitutive model is used for modeling the soil plasticity. Comparison indicates that the present numerical results match well with the derived slip-line solutions. According to the obtained vertical load-displacement curves, concurrently referring to the plastic strain field and the soil incremental-displacement vector field, the shear failure types and the corresponding collapse loads can be thereby determined for the pipeline foundations on clayey soils.