Effect of surface roughness on axial soil-pipe interaction: a discrete element approach

The Discrete Element Method (DEM) is a valuable tool for understanding axial soil-pipe interaction (ASPI) using micro-mechanical analysis. Previous DEM studies did not simulate interface roughness, a crucial factor in ASPI, by using flat facet discrete elements for the pipe surface and excessive scaling factors for soil particle size. This study presents a novel approach using 3D DEM with a linear contact model, including rolling torque. Pipes are modelled with overlapping spheres to simulate adjustable surface roughness. To eliminate boundary effects, periodic walls are applied along the axial boundaries. Optimised domain thickness and particle refinement methods improve simulation efficiency and accuracy. The axial behaviour of pipes with varying roughness levels and burial pressures was simulated to back-analyse physical modelling. The computed macro-mechanical behaviours, including axial force, settlement, interface contact pressure, and stress path, align well with the trends of experimental results. Distinct soil particle displacement patterns around rough and smooth pipes lead to different ASPI mechanisms. Soil particles move axially in sync with the rough pipe, causing significant volumetric expansion within the interface shear band, increasing interface contact pressure, and compressing the surrounding soil. This movement strengthens soil arching by forming stronger force chains from the pipe crown and invert. Conversely, limited shear strain around smooth pipes results in slight volumetric contraction, causing surrounding particles to move inward and reducing the interface contact pressure. Finally, parametric studies on surface roughness effects illustrate that, within two critical normalised roughness levels, axial resistance increases with roughness. Beyond this range, axial resistance remains almost constant.