CONCRETE RING
The concrete ring construction basically consists of a vertically positioned cylinder that is filled with concrete, stone and rebar. Depending on the depth between the bottom and the bedrock, the concrete rings can be sunk into the sediment and rest on the bedrock with the help of piles or placed directly on the bedrock if it is shallow enough. If the sediment is more than a couple of meters, the rings are usually left to rest on the rock with the help of stakes that reach all the way down. The rings are placed in these cases on beams placed on the bottom where the rings will stand, the beams help to fix the piles and give initial stability to the rings while filling them with stone and concrete. If the depth allows the rings to be placed correctly on the rock, one usually drills a few holes in the rock and anchors rebar in it.
Concrete ring is a relatively cheap solution that provides good stability, but with limitations if the dimensions are not significantly enlarged. Many consider the appearance to be a disadvantage, which probably means that the construction is not so common these days.