“…with about 2,000 of such rigs operational in the world at present.”

If we hadn’t suspected something was wrong before, we’d know it when we got here.

The total number of jackup drilling rigs in the world is 527, not 2000.

Your sources have given you some bad material.

Jackup mobile drilling rigs use spud cans which, even though they look something like this, aren’t. Spud cans are meant to penetrate only as far as required to support the weight of the rig and equipment. This penetration is achieved by “preloading” the rig with ballast, weight, to force the can into the seabed until it reaches stability.

These things you’re writing about aren’t spud cans, they’re large diameter pilings installed using the weight of the water column above them instead of being driven to bedrock. At the depths you’ve mentioned, the water above these piles will weigh close to a million pounds.

Therein lies the only novelty in this design — the method of installation; instead of using a hammer or ballast, this method uses the weight of the water column to drive the pile.

In this case, the reason 8 meters of penetration is adequate is because of the extremely large diameter of the pile, not because of the “suction” underneath.