Basalt columns and crack formation during directional drying of colloidal suspensions in capillary tubes

Formation of basalt columns during cooling of lava may be modeled by the drying of colloidal silica suspension confined in capillary cells (Allain and Limat 1995, Gauthier et al. 2007). During the drying process, particles aggregate at the open edge forming a growing drained gelled porous medium. High negative capillary pressure in the draining fluid (Dufresne et al., 2003) and adhesion to the walls of the cells generates high tensile stresses in the gel leading to crack formation. Depending on the experimental conditions and the shape of the cell (rectangular or circular), several crack morphologies appear. Here the aim is to compare the experimental morphologies with the ones predicted by fracture mechanics. For this purpose, the drained gelled porous medium is modeled by a linear elastic medium subjected to tensile prestresses and the cracks by the variational approach to fracture of Bourdin, Francfort and Marigo (1998, 2000, 2008).