Numerical modeling of oblique pipeline-soil interaction in dense sand

Buried pipelines are a safe, economical and efficient way of transporting oil and gas in both onshore and offshore environments. The pipeline generally passes through a wide variety of soil, and is buried at varying depths to maintain the flow of hydrocarbon by minimizing heat loss and avoiding interference with other human activities. Pipelines are usually installed in a trench and then backfilled with loose to medium dense sand. This backfill materials might be densified due to natural phenomena such as wave action at offshore shallow water depths. During operation, the pipeline might be subjected to loads resulting from oblique movement through the soil. The force/resistance due to relative displacement between soil and pipe during oblique movement is an important parameter for safe and economic engineering design. In the present study, an advanced numerical analysis is conducted to understand the pipe–soil interaction during oblique loading in dense sand. The Mohr–Coulomb (MC) and a Modified Mohr–Coulomb (MMC) are used for numerical analyses. Showing the limitations of the MC model, the advantages of the MMC model are shown for oblique loading cases. The importance of boundary conditions in the oblique loading analysis is shown. This study also focuses on the problems of current design practice where soil is represented as spring. It shows the importance of developing a new guideline for oblique loading, showing the limitation of ALA and PRCI guidelines. Large deformation finite element analysis is performed using the Arbitrary Lagrangian and Eulerian (ALE) method. The necessity of post-peak analysis is shown via yield surface formation for geohazard analysis. A parametric study is performed to show the effects of different oblique loading angles, diameters and embedment ratios on the force/resistance due to relative displacement between soil and pipe