Fig. 4. Drainage of APS-6.0 sample during multistep experiment (a) p = 0 cm; (b) p = 24 cm; (c) p = 79 cm; (d) p = 490 cm. Horizontal slice at 13.73 mm from the bottom. In these and all other gray-scale images the white or light areas represent the water phase, black is air, and the gray areas are sand grains.