How to shorten a concrete pipe sticking from ground

Question

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.

Answer 1

There exist dedicated concrete cutters. For example the Stihl TS 420 has about 12cm cutting depth. I don't know if those saws allow horizontal cutting.

A preferred solution would be to simply raise the soil if the grading allows it

Answer 2

My answer assumes your local ordinance permits you to achieve your goal.

1. Mark the inside perimeter with a sharpie or paint line for guidance
2. Use a masonry bit to drill a few holes next to each other along the paint line
3. Insert a concrete reciprocating saw (Sawzall) blade into the holes
4. Make your cut all the way around
   • Reciprocating saw required
   • Don't worry about the dirt, that's only an issue for regular wood blades
   • Make use of small wedges so that the concrete doesn't eventually bind your blade
5. Lift off the excess concrete shaft
6. Use a diamond grinding cup to smooth out imperfections
   • Angle grinder required
7. Chisel and grind out additional concrete to fit a manhole cover

Concrete reciprocating saw blade:

Diamond grinding cup:

Answer 3

Obviously, with a cutting wheel, you would cut around the outside, as deep as possible. 6cm, you say. That will cut through at least some of the concrete wall. Don't forget to stuff a cushion or something inside, to catch any debris!

Then, attack what's left of the wall from inside, assuming the tool is short enough to get into the aperature. If not, two stages are called for.

1. Cut at an angle to reach the right level on the outside.

2. use the angle grinder/cutter to level off the rim from the outside. Level with the original, hopefully horizontal, cut.

If not, a 'last ditch!' effort of bringing the ground level up would work, over several yards.