| We report a study of the paths formed by a finite volume of air gently injected at the base of an immersed granular material. A two-dimensional model, based on experimental observations, shows that the typical height and width of the region explored by the branched path depends not only on the injected volume V , but also on a dimensionless parameter χ which accounts for the relative effects of the gravity and capillarity. For a given injected volume V , larger gravity effects lead to taller and narrower structures; for a given χ , the typical height and width of the structure scale like V 1/2 and V 1/4 , respectively, while the typical gaseous fraction in the corresponding region increases accordingly like V 1/4 . Such results can be of practical importance: For instance, gas can be trapped on purpose in an underground natural container below a granular slurry. Our results can help in predicting if the gas is likely to reach the free surface and escape the system if the container presents a defect (hole or fracture). |
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