An Open-Source 3D Soil Printer for Physical Modeling and Element Testing

High-quality physical modeling and laboratory element testing of reconstituted granular materials rely on the creation of models and test specimens to specific properties with repeatable and reliable structure and shape. Ideally, identical models and test specimens are created with precise and accurate, homogeneous or heterogeneous properties such that repeat tests provide consistent outcomes. Recently, automated 2D and 3D printing capabilities have been developed and applied to many industries, including soil printing using air pluviation; however, all currently available soil printers are unique to their location of development or only available commercially, both of which limit distribution and further customization. In this paper, a fused deposition modeling 3D printer is modified to create an open-source, automated, and scalable 3D printer for granular materials. Well-established air pluviation principles using the combined effects of drop height and mass flow rate to achieve a target soil density are combined with additional options to create customizable shapes (i.e., slopes) as well as geological bedforms such as cross-bedding. The Royal Military College 3D printer can construct repeatable and replicable models/specimens up to a size of 40.0 cm × 48.5 cm × 34.0 cm in terms of length, width, and height, over a wide range of relative density (45–100 %). Internal consistency in soil prints is confirmed through vertical as well as lateral density tests, showing variation less than 0.4 % and 0.8 % from mean values. Consolidated undrained triaxial tests performed on three repeat test specimens display nominally equivalent stress, strain, and pore pressure response up to shear band development. Included in the supplementary information are a complete parts list, design drawings, printer manual, guidance for construction, python code, and example videos of model prints.