Study of Trench Backfill Particle Size Effects on Lateral Soil Restraints on Buried Pipelines Using Discrete Element Modeling

Soil restraint development during relative ground movements is an important consideration for assessing the integrity of buried pipelines. Evidence from full-scale experiments suggest that the relative backfill particle size with respect to the pipe size may influence the development of lateral soil restraints. In experiments in which pipes buried in uniform significantly coarse-grained soil backfill were subjected to relative movement perpendicular to the pipeline alignment, the lateral soil restraint increased to a peak value and the backfill experienced a block-type failure mode; with increasing displacements, some of the backfill mass disintegrated and flowed as individual particles, leading to a postpeak reduction of lateral soil restraint. When pipes in backfills with relatively small particles were subjected to relative lateral movement, the backfill moved as blocks, without disintegration as individual particles. It was shown that full-scale soil–pipe experiments can be effectively simulated using numerical discrete-element modeling (DEM), including the particle-size effects on the lateral soil restraints and ensuing soil failure mechanisms. Using the DEM work, considering a range of pipe diameters ($D$), burial depths ($H$), and mean backfill soil particle sizes ($d$), it was possible to delineate $(H/D)\text{-}(D/d)$ combinations that constitute pipeline configurations leading to significant postpeak reduction of lateral soil restraint during ground movements—a useful consideration to select optimal backfill materials to reduce soil forces in pipeline design.