Effects of sample preparation methods on initial sand fabric: X-ray CT exploration

Initial soil fabric directly influences the soil’s mechanical behaviour. Different methods have been used to prepare samples in the laboratory by mimicking soil formation processes in natural or man-made conditions. However, in-depth investigations into how the initial soil fabric might change with different preparation methods are lacking, hindering selection of proper sample preparation methods when studying fabric evolution effects and calibration of initial soil packing conditions in discrete element-based modelling. Enabled by in-situ X-ray computed tomography (CT) imaging, three-dimensional initial fabrics of samples prepared by six commonly used methods were systematically investigated. Packing density, uniformity, non-directional and directional descriptors were quantified. Air pluviation, dry deposition, wet deposition, and dry tamping methods produced samples with a uniform local e, with the particles of air pluviation samples being more horizontally arranged. Dry tamping, moist tamping and static compaction produced less anisotropic samples as their particles and contacts were more randomly arranged. Unsaturated samples had less uniformity and anisotropy due to capillary-induced aggregation, especially for soils composed of an-gular particles. Increase in compaction energy led to an alignment of contact normal vectors towards the vertical direction, but its influences on the particle orientation and branch vector orientation changes were limited.