Whether you pour concrete for a walkway or patio, a strong gravel base is required to prevent the concrete from cracking and shifting. Gravel is especially important in clay soil because it doesn't drain well, which results in water pooling under the concrete slab and slowly eroding the soil as it finally drains.
Can I pour concrete directly on dirt?
Long story short, yes you can pour concrete over dirt.1 jul 2020
How do you prepare the ground for a concrete sidewalk?
https://www.youtube.com/watch?v=h7tIjBEPiPU
What is the best material to put under concrete slab?
Overall, a mix of crushed stone and stone dust is the best base material for any concrete flatwork. It all comes down to the ground and soil you will be working with.