system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If you have a small leak from a container full of sand (could be a few tons even) you can shut it by spraying a bit of water on the hole,how does this work? why is the huge mass of sand doesn't push out the wet sand on the hole?
gpt
So first thing to mention is that sand isn't a liquid, it's a particulate solid. If it were water in that container, and you tried to plug it with sand, then it would absolutely be forced out. That's because water is far more fluid than sand.

Sand will naturally compress down to form what almost resembles a solid, even when completely dry. Sand particles aren't perfectly smooth, and have friction, which means the particles don't easily move past each other when compressed. The particles need space around them to move. If you take some sand and "pour" it from one container to another, there's a lot of air in there that allows the particles to move around each other and "flow" as though it's a liquid.

In your example, the tons of sand in the container are compressed under their own weight. The hole at the bottom is not under great pressure, because the sand has, for all intents and purposes, "solidified" and won't flow easily, so there's very little pressure at the hole.