Understanding the mudcrack patterns: How layer thickness, grain size, and secondary layers affect their formation – A laboratory study

This paper investigates the initiation and evolution of polygonal crack patterns in desiccating soil layers with varying thicknesses and grain sizes, both with and without a secondary saturated sand layer placed beneath the soil layer. Single-layer experiments involved soil samples within a specific range of grain sizes (0–100, 100–300, 300–500, and 500–850 μm), maintaining soil layer depths at 10, 20, 30, 40, 50, and 60 mm. In double-layer experiments, a saturated sand layer was introduced below the soil layer to check the role of relative layer thickness on crack patterns. Time-lapse photography captured surface crack development during desiccation, allowing for the measurement of geometric parameters like crack width, crack intensity factor (CIF), and intersection angle (CIA). The single-layer models indicate an increase in crack width and CIF with greater layer thicknesses, while CIA decreases with increased layer thickness. Additionally, experiments with finer grain sizes exhibit relatively wider cracks, along with higher CIF and CIA. In double-layer models with varying thicknesses of individual layers, crack growth is found to be independent of the upper soil layer's thickness. Instead, crack propagation is controlled by the lower sand layer, as the supply of water from the lower sand layer to the upper soil layer facilitates prolonged desiccation, resulting in larger CIF values. Using digital image processing and the box-counting method, we calculated the fractal dimensions (D) of the cracks were calculated. D demonstrates positive relationships with grain size in both single- and double-layer experiments, suggesting a self-similar evolution of crack patterns in the models with coarse-grained soil.

The role of basal water-rich sand layer in the growth of mud-cracks is investigated.