Quantification of soil shrinkage in 2D by digital image processing of soil surface

Knowledge of soil shrinkage behavior is needed to improve the understanding and prediction of changes of unsaturated hydraulic properties in non-rigid soils. The heterogeneity and interaction of horizontal and vertical soil shrinkages that produce soil cracks and associated soil subsidence require additional quantification. Vertical shrinkage can be calculated easily by soil height with vernier caliper. However, a quantitative and feasible measurement of horizontal shrinkage has not been developed yet because of the complicated and irregular geometry of soil cracks. This paper introduces a new method to measure soil cracks non-destructively and continuously by digital image analysis. Using Adobe Photoshop and Windows Scion 4.02 image processing, the proposed procedure accurately identifies changes as small as 1.0 mm² and shows differences even when areas of soil cracks were increased by as little as 1%. Various geometry factor values indicated soil shrinkage in the two dimensions was anisotropic during the whole drying. During initial dehydration from saturation, only subsidence shrinkage could be identified. With the further dehydration, the soil cracks developed and increased in size. These results suggest that the heterogeneity of soil shrinkage in 2D should be taken into account when modeling the total soil shrinkage behavior and associated unsaturated hydraulic properties.