Abstract: Vertical upheaval buckling is a critical instability mode in buried pipelines and poses substantial risks to pipeline safety. Most prior studies have focused on upheaval behavior under flat terrain, with limited attention to failure mechanisms on slopes. In this study, model tests of buried-pipeline upheaval on slopes were conducted using distributed fiber-optic sensing and particle image velocimetry (PIV). We systematically analyzed soil deformation and failure mechanisms, and the mobilization of uplift resistance, under varying slope angles and burial-depth ratios. The results show that, 1) Increasing slope angle gradually reduces the soil’s peak uplift resistance, while higher burial-depth ratios significantly enhance both peak and residual uplift resistances. 2) Regardless of slope angle or burial depth, the pipeline displacement at the onset of residual resistance is approximately 0.2D, where D is the pipe outer diameter. 3) During the uplift process, the pipe cross-section undergoes ovalization, and a wedge-shaped failure zone forms in the overlying soil. Based on these findings and Mohr’s circle theory, we propose a method to calculate the peak soil resistance of pipelines under slope conditions. These findings advance understanding of soil–pipeline interaction on sloped terrain and provide theoretical and practical guidance for the design and safety assessment of buried pipelines in complex geological settings.

Key words: buried pipeline, optical frequency domain reflectometry (OFDR), particle image velocimetry (PIV), soil-pipe interaction, soil resistance