Pouring concrete directly onto the ground is possible, but it's not recommended. To ensure the best results, the soil must be properly prepared and leveled before pouring. This includes removing loose dirt and compacting the subgrade, as well as adding a gravel base to support the additional load of the final slab if necessary. The composition of the concrete is also important, as it plays a role in the overall strength of the concrete once it has set.
However, it's important to note that repairing and maintaining a concrete slab may be more expensive in the long run than caring for a pillar-and-beam foundation. When waiting to pour concrete, the goal should be to ensure that the floor is compact enough to keep the concrete stable, and that there is no more room for dirt to settle and that the concrete has room for it to “wobble”. Place reinforcing bars at all the center points of your foundation and design a concrete mix according to your needs (the ratio of aggregate and concrete). Construction experts consider the subgrade layer to be the most important when it comes to determining the load that the concrete slab will be able to withstand.
In short, concrete can only be as strong as its subgrade layer. Whether you're pouring a yard, a base for a shed, or some other concrete project, it's essential to take all necessary steps before the concrete truck arrives. This includes preparing and leveling the soil, adding a gravel base if necessary, and designing a concrete mix according to your needs.