Limit loads for pipelines and cylinders partially embedded in frictional materials

Accurately assessing the forces and reactions on cylindrical objects partially embedded in soils is fundamental in pipeline engineering as well as the analysis and design of off-road vehicles. With a view towards understanding the limiting forces acting over the contact area between the cylinder and the soil, this paper compares two different theoretical approaches for predicting ultimate loads under combined vertical and horizontal loading. The first is an approximate method based on idealizing the contact interface as a flat shallow strip footing, and the second is based on finite element limit analysis (FELA). Focus is on purely frictional material and plane strain conditions, assuming a rigid cylinder and perfectly plastic material obeying the Mohr-Coulomb yield condition with associated plastic flow. The approximate method based on an analogy to an equivalent shallow foundation (with no overburden) predicts results that are reasonably close to those from FELA but only when small embedment is considered. Moreover, the discrepancy between the two approaches for the case of free cylinder rotation is attributed to the existence of a contact moment over the soil-cylinder contact interface. Practical implications for pipeline engineering and off-road vehicle engineering are discussed.