Undrained Load-Displacement Behavior of Partially Embedded Pipeline on Seabed

Abstract

The initial embedment of as-laid offshore pipeline is one of the important design considerations for on-bottom stability analysis. Despite the significant advancement in the use of numerical and analytical methods to predict the as-laid pipe embedment, there is still a lack of understanding about the governing parameters and their influence on the behavior of the pipe-seabed system. In the present paper, a two-dimensional plane strain finite-element model was developed to study the influence of the properties of seabed soil on the pipe load-deformation behavior subject to undrained soil conditions. The model was developed using commercially available finite-element software. The seabed soil was considered to behave as an elastoplastic material following the Mohr-Coulomb yield criterion, while the pipe was modeled as a rigid element. Both continuous and wished-in-place loading were performed up to displacements of 0.5 of the pipe diameter. The influencing parameters, including elastic modulus, shear strength, submerged weight of the seabed soil, pipe diameter, and berm growth, were studied with respect to the vertical collapse load and change in embedment. The results obtained were compared with results reported in the literature, and the parameters that have the most significant influence on the pipe behavior were identified. Results indicated that the heave formation significantly depends on the weight of the soil, and an analytical model was developed to predict the pipe load-displacement behavior, incorporating these factors.