Uplift of Pipelines Buried in Rockfills: Significance of Particle Scale Effect

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4. Uplift of Pipelines Buried in Rockfills: Significance of Particle Scale Effect

ABSTRACT: Quantification of uplift response of a pipe through overlying backfill materials is critical for assessments such as pipeline upheaval buckling (UHB) and on-bottom stability. In lieu of project specific physical model tests, recommendations from DNV-RP-F114, regarding the dimensionless resistance factor (f) and the mobilisation displacement for the peak resistance, are often adopted for design. However, published testing results indicate that those recommendations may not be always appropriate, especially for rockfills. The ratio of characteristic length such as pipe diameter or overlying material thickness (H_top) to median particle size (d₅₀) is believed to significantly influence the mobilisable uplift resistance and the corresponding displacement, a phenomenon known as the 'particle scale effect'. This study compiles relevant physical model test data to establish a comprehensive database, facilitating derivation of the uplift resistance and the corresponding mobilisation displacement. The database is further augmented with results from a series of numerical simulations using the Discrete Element Method (DEM). The compiled data reveals a non-linear relationship between f and D/d₅₀, while the correlation between f and H_top/D is less distinct. Similar trend is also found between the mobilisation displacement and D/d₅₀. For design purposes, low estimate trendlines have been proposed. The findings suggest that the particle scale effect is particularly pronounced for small D/d₅₀ ratios, indicating large backfill particle sizes relative to the pipe diameter. Consequently, numerical methods based on continuum mechanics should be used with caution when dealing with pipe-rockfill interaction scenarios.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

15 - Mooring lines, Cables, Pipelines, Immersed tunnels and Risers