The crack pattern of indented cohesive granular media

Cohesive granular materials, like wet sand, retain their shape before yielding under stress. This solid-like behavior is associated with elasticity. As the loading increases, the material typically flows. However, cohesive materials can also develop cracks, similar to those observed in brittle materials. This study explores the formation of cracks during the indentation of a granular pile. A solid cylindrical indenter is pushed quasi-statically into the wet granular medium, causing radial cracks to appear. These cracks resemble mode I cracks observed in brittle solid materials. We characterize the crack pattern through direct observation and three-dimensional X-ray micro-tomography. Notably, we highlight the correlation between the dilation of the material during shearing and the appearance of cracks.