My idea to plug the pipe.
I am a mechanic with the Canadian Armed Forces and have worked around heavy equipment for many years. When I heard we could post Ideas, I came up with something that I hope will work.
There is industreal air bags that are used for flipping trucks back on their wheels after an accident, very little air in these bags creates huge amounts of force. I'm not sure how much pressure is ccreated when you try and plug that pipe but my idea is to attach one of these bags to a rod, lower it in the pipe as far as needed inflate bag till leak stops then fill with concrete and let set, simple solution but those are the ones that usually work best.