I misunderstood your explanation. probably because you've over-thought the whole thing pretty severely. oddly enough, you've missed a few important factors.
Concentrating the entire weight of a fairly robust person into a spot the size of a coin would embed the coin pretty deeply into the ground.
I'm assuming a coin the size of a silver dollar, 1.5 inches. 98kg is bout 216lbs, concentrated onto a point an inch and a half across, that's several times the amount of force needed to embed a steel spike in a concrete block.