If the foundation has the shape of a cylinder, then an iron, ceramic or asbestos -cement fixed formwork is needed.
If the shape is made under the grillage, then it will be located at a certain distance from the surface of the earth, therefore, in the design it is necessary to fix the corners of the tape below qualitatively, otherwise the solution will partially spill. And inclined supports in this case will be longer, and their ends will rest against the ground.