A comment
There was an idea to make a bathhouse a 3x3 meter log house. A base with another 3 meter outlet. A friend advised to make a permanent formwork from a pressureless asbestos-cement pipe with a diameter of 200 mm, wrapping it with roofing material on the outside. After my reasonable question, why not just pour concrete into the selected hole, and limit the last 50 cm with a pipe.The answer was that adhesion of the soil to a smooth asbestos pipe, also wrapped with roofing material, will significantly reduce the effect of heaving soils on the pile. Therefore, a depth of 1.5 m was chosen with a freezing level of 1.2 m.
As a reinforcing cage, a spatial lattice was chosen with 6 vertical rods of 8 m diameter and horizontal dressings at a distance of 60-70 cm. In principle, reinforcement of 4 10-12 mm or 3 12-25 mm of rods was allowed, but for a cylindrical shape, the load distribution to the external side more productive.
pros
Relatively low cost with considerable strength
Average labor costs.
Minuses
Not suitable for all types of soil.