In the garden I have an access shaft for underground rainwater tank. The shaft itself is a concrete pipe outer diameter 72cm and internal diameter 56cm. The wall thickness varies between 6 and 10 cm (the hole is not centered).
What is the best way to shorten it so it end below the ground level? I want to install proper manhole cover, and I do not like how it is sticking out so much.
Option 1 would be with big grinder w/ concrete blade, but the biggest I could rent will cut only 6cm. Also I would have to dig a wide trench, to get access to the below grade.
Option 2 would be to drill series of hole around the perimeter of the pipe, and then use chisel and wedges to break the top ring off.
I am more comfortable with #2, but I am not sure if there is a risk of breaking the whole pipe. From what I was able to see there is no steel reinforcement in the concrete.