A real granular sim — grain-by-grain contacts, friction, and capillary cohesion. The angle of repose and wall-holding emerge; nothing is faked with a slope rule.
Tool
Drag in the pit. Disturb shoves grains, Water wets them (watch walls firm up, then turn to mush if you flood it), Dry removes moisture.
Granular physics
Capillary cohesion (wet sand)
Cohesion is non-monotonic in moisture (Hornbaker et al., Nature 1997): ~0 when dry, peaks at intermediate wetness, collapses when saturated.
Water
World
“Tilt test” drops a tall block so you can watch it slump to its natural angle.