78th Annual Meeting of the APS Division of Fluid Dynamics (Nov 23 — 25, 2025)

V025: Dry pockets to sinkholes: Fluid pathways in granular beds

Capillary-driven imbibition and subsequent drainage of a polymer granular bed were visualized using a high-speed camera operating at 250 fps. During imbibition, distinct phenomena such as local granular convection and the collapse of local voids were observed. The packing density and local heterogeneity of the bed were found to be critical for anomalous dynamics, indicating that even minor structural weaknesses can cascade into large-scale instabilities. In contrast, during drainage, variations in experimental parameters yield negligible differences in the overall behavior. This insensitivity arises because the prior imbibition process induces bed realignment, thereby alleviating local structural heterogeneities. These findings are fundamental to elucidating the mechanism underlying bed clogging and may provide new insights into the formation of the sinkhole.