Micromechanical analysis of pipeline-soil interaction in unsaturated granular soil undergoing lateral ground movement

The micro- to macro-scale pipeline-soil interaction mechanism in unsaturated granular soil remains unclear. This study investigates the unsaturated suction effect on the pipeline-soil interaction undergoing lateral ground movement using coupled discrete element method and finite element method (DEM-FEM) simulations. The Johnson-Kendall-Roberts (JKR) adhesive model was used to simulate the interparticle suction while the pipe segment was simulated with finite element meshes. The findings reveal that discontinuity and large deformation occurrences in unsaturated sandy soil in model tests can be successfully modelled by the DEM-FEM method. Besides, the interparticle suction effects on contact forces, particle collision behaviours, and special soil pressure distributions near the pipeline-soil interfaces were discovered and successfully explained. Additionally, progressive soil deformation and failure behaviours in dry and unsaturated soils were compared while the partial similarity between the suction effect and buried depth effect on pipeline-soil interaction was discussed. Finally, several conclusive pipeline-soil interaction failure patterns in different interparticle-suction conditions were identified after analysing a series of particle-scale behaviours including particle trajectories, particle contacts, and particle rotation distributions. The study indicated that neglecting the unsaturated effect can result in severely underestimating the intensity of pipeline-soil interaction and misjudging the soil failure patterns.