Horizontal Soil Resistance of Exposed Pipelines in Sand Wave Areas: Experiments and Upper-Bound Analysis

Current research on the horizontal soil resistance of exposed pipelines assumes that the pipeline is embedded in a flat seabed, where the horizontal restraint of the pipeline by the seabed is primarily determined by the depth of its embedment. However, in one section of the shelf sea, the seabed exhibits undulating sand waves. First, the presence of sand waves affects the lateral restraint of the pipeline; second, sand wave migration changes the pipeline’s embedment, which affects the horizontal restraint. In this paper, a large-scale indoor plane strain modeling test and a particle image velocimetry (PIV) observation test were performed to address the problem of the horizontal soil resistance response of exposed pipelines in the sand wave zone. Additionally, a large-deformation numerical analysis model for the horizontal interaction of exposed pipe–soil in the sand wave area has been developed. The variation rule of soil resistance for the exposed pipeline was thoroughly analyzed, and a new upper-bound solution was established as a result. The results show that the influence of the initial soil berm on soil resistance mainly includes overcoming the gravity of the berm and increasing the passive soil resistance, and the influence of the spacing distribution of the soil berm on soil resistance is observed to range from 0 to 1.25 times the diameter of the pipe, in which the maximum value of soil resistance is taken in the case of a berm layout of 0.25D, which is increased by 69.83% compared with the case of flat seabed. It is clear that the spacing distribution of the berm and the pattern of change in horizontal soil resistance, as well as the change in the berm’s volume inside the sand soil slip surface in front of the pipe, are correlated.