Drain pipe addition

After several rain, I noticed a pond in my backyard. I made a concrete patio last summer with drain pipes underneath it. So, I dug some soil and got the one end of the drain pipe where two pipes are connected by a 90 elbow. Both pipes don't move at all as they are under the concrete. What I have to do is to somehow replace the elbow with three way connector so that I can add another pipe to it. Since two pipes don't flex, I cannot even remove the elbow. Any tricks to replace the elbow with three way connector without damageing pipes? Appreciate your advise.

I assume the pipe is PVC or ABS. In either case, if you want to change or add to the existing system, you will have to cut the old fittings off and add whatever new ones are necessary to do what you want to do. This might be a place where you could use no-hub connectors. You can not disassembly PVC or ABS joints as they are solvent welded. There are numerous PVC and ABS fittings available which will allow you to do almost anything. I would caution you to be certain there is adaquate slope to the drain pipes or they will not drain. The standard slope for household drains is 1/4" per foot. If this is rain water that is being drained, you need to take precautions to keep trash out of the pipe, and it would be wise not to use elbows at all. If you must change the direction of a pipe, us two 45 degree bends or a long sweep 90. No sharp corners.

Thank you, Gary, for your advise. Yes, I am talking about rain drain pipes made of white PVC (looks like 4" in diameter). I went a nearby HW store and found a rubber connector with two metal screwed-clamp on each end. This might work even though two main pipes don't flex. Now my question is if it is all right to use this rubber connector underground or not.

That is a Fernco coupling. They are not supposed to be used underground although it would likely last for many years. There is no pressure on a drain and in this application with only rainwater in the drain, a small leak 20 years from now wouldn't be a disaster. If you can see how to make the connections you want to make using the Fernco, go for it.

We use Fernco fittings underground here all the time. We arent allowed to use no hub bands underground though.

I may have misunderstood. Thanks for the correction.

Thank you everyone for advise. A minor leak 20 years later is not a problem. I won't be around then anyway !I will be watching whoever takes over my house dealing with it from the sky.