One stroke of
good luck that day, was the fact that there was a technician on site, doing routine maintenance work on the sprinkler system. In fact, the system was under only static pressure--the pressure of the city water main that fed the site. Also, since he was working on the system, the alarm system was disabled--otherwise, we'd have had firetrucks rolling as soon as the water started moving through the sprinkler system.
One of the guys went running to find the fellow in charge of grounds maintenance, so we could get in and shut off the water. (There was no valve outside the building--a wise precaution against somebody inadvertantly shutting down the sprinklers while trying to shut down something else.) The guy looking for the mauntenacne man was met at the door by the sprinkler tech, who expressed surprise at the fact that, as he worked, all of a sudden the pump started turning as if by magic. (Our opening of the pipe had allowed the water to run through, spinning the pump.) Once he understood what had happened, he shut the whole mess down pretty quickly.
We dug around the end of the 8" pipe, and found a bell, with about a 2 foot piece coming out of it, and a cap on the end. Since it would've been in the way of the future manhole, we took the piece out, and put a plug in the bell. This was secured by a retaining clamp, behind the bell, with two pieces of threaded rod holding a bar across the plug. All bolted up nice and tight, there was no way that plug was going to push out of there, even without a thrust block. Right?
Now, the sprinkler system had a "jockey pump" that kept it charged at whatever its specified operating pressure was. (I'm thinking 190 PSI, but it's been a few years.) Keep in mind, that this system was designed to be able to push water up to the top of a six story condo building.
The tech put the system back online, and came back outside. We all stood and watched... Ever so slowly, the threaded rods began to bend, and the plug backed out of the bell, maybe half an inch, and then stopped. Everyone began to breath again. Until we watched the entire end of the pipe move six inches...
Just about that time, we were interupted by a roar, from the side of building #1, and a puff of black diesel exhaust. Had I mentioned that this whole system was powered by a 6 cylinder Cummins?
About 18 feet back (the length of a section of ductile iron pipe), a geyser erupted from the lawn.
That Cummins had been patiently waiting for the chance to do what God had intended it to do, and it wasn't going to be denied. The jockey pump had pushed the next joint back right apart, and the diesel took over from there.
The tech took off at a dead run for the pump room, and by the time he got it shut off there was two feet of water against the basement garage door of building #2.
We dug that section of pipe out, and re-installed our plug assembley, but this time we poured a yard of concrete against it, and left the backhoe bucket pushing against it all night til the concrete was hard enough....