Micromechanical analysis of upward pipe-soil interaction behaviors in unsaturated granular soil

The micromechanical mechanism of upward pipe-soil interaction in unsaturated soil remains unresolved. This study investigates the upward pipe-soil interactions in dry and unsaturated granular soil through a sequence of coupled discrete element method and finite element method (DEM-FEM) simulations. The capillary suction effect was simulated using the Johnson-Kendall-Roberts (JKR) adhesive model, while the pipe segment was simulated with finite element mesh. A comparison was conducted between the behaviors of pipes and soil in dry, unsaturated soils at various depths of burial. The findings reveal that discontinuity and large deformation in unsaturated granular soil can be modeled successfully. In addition, the capillary suction effect on the stress and deformation of pipes is effectively explained by the wide contact force distribution and the weak particle collision behaviors around pipes. Meanwhile, the study identifies differences in soil arching effects as the essential reason behind the different modes of soil deformation in dry and unsaturated soils. Moreover, an exploration of particle-scale behaviors yields several conclusive mechanistic modes of upward pipe-granular soil interaction at different burial depths. The study demonstrated that suction in unsaturated granular soil significantly improves the upward pipe-soil interaction force and changes the failure mode of pipe-soil interactions.