The difference between foundation cushion and foundation is that the foundation cushion is set below the foundation, and the top of the cushion is in contact with the bottom of the foundation.
Foundations are divided into brick foundations, concrete foundations and reinforced concrete foundations according to materials.
According to the shape, strip foundation, independent foundation, raft foundation, etc.
But the soil is not like this. When it meets water, it will liquefy and its strength will decrease. If the strength is reduced, the newly poured concrete will be deformed before hardening. Therefore, it is better to use gravel as cushion than to use soil as cushion directly. Similarly, cement mortar is used to build bricks, just like concrete.