Laboratory Model Testing and DEM Simulation of Bearing Capacity and Localized Deformation in Uniformly Graded Sand

Ground bearing capacity and localized deformation beneath shallow foundations remain important problems in geotechnical engineering. This study examines a rigid rectangular footing (70 mm × 50 mm) on dry, uniformly graded sand (d50 = 3.0 mm; Cu = 1.3; Cc = 1.0) using a laboratory model test, DIC-assisted imaging, and DEM simulations with single-sphere and four-sphere clumped particles. The selected experimental bearing pressure was 561.00 kPa at 20.62 mm settlement, based on the maximum-curvature criterion, equivalent to 29.5% of the 70-mm footing dimension. Visible deformation zones were estimated to orient at 44.33° and 48.80° on the left and right; these are approximate image-based directions, not theoretical slip-surface angles. The DEM simulations gave ultimate pressures of 445.57 kPa (single sphere) and 527.87 kPa (clump), 20.58% and 5.91% below the experimental value, respectively. Since the two DEM representations were calibrated separately and used different material/contact parameters, the closer clump-model agreement cannot be attributed to particle shape alone and is not an independent validation. The results are model-scale observations affected by the container boundaries and should not be directly extrapolated to full-scale design.