My concrete drive has a section approx 3m square which has cracked and sunk with a hole appearing where a bit has broken off, looking into the hole it appears there is a cavity underneath the area which is all cracked the rest of the drive way is fine. Could this be caused by subsidence? my idea is to cut out the cracked area put a 6 inch hardcore base down then replace with new concrete, my question is is it as simple as cutting out damaged area putting sub base down with a wacker and pouring new concrete in or am i missing something?