Expansive clay

Okay kiddo, let's talk about something called "expansive clay." Clay is a type of dirt that is made up of lots of tiny particles. Sometimes this type of dirt can be pretty special - it's called "expansive" because it can change a lot when it gets wet or dry.

When the ground that's made up of expansive clay gets wet, the clay particles start to stick together really well. This means the dirt can swell up, almost like a balloon filling with air. But if the dirt dries out again, the clay particles will start to pull apart from each other - kind of like deflating a balloon.

This swelling and deflating can be a big problem for buildings, roads, and other structures that are built on top of the ground. When the ground swells up, it can push buildings or roads upwards, causing cracks and damage. But when the ground deflates, it can cause everything to sink down, also causing damage.

So, sometimes people who are building things in areas with expansive clay will have to do special things to make sure their building or road doesn't get damaged by all the swelling and deflating. This might involve digging really deep down into the ground to put in a strong foundation, or doing something else to help the ground stay stable.