A nearby town had a water main break yesterday, and I just happened to be there when it broke. It was quite impressive! It began under a huge pile of snow from a parking lot, and that 8 foot pile of snow just melted into the flowing water, and vanished. Another guy who was watching it, (who had called the fire dept. about it), jokingly said "that's a great way to get rid of snow". Anyhow, I watched the city guys dig up the pipe, from my car, and heard one of them say "it split in half".
Anyhow, it appears that pipe breaks tend to occur much more often when the temperature drops far below zero, (which it had just done over the last several days).
But I cant understand why this happens...... These pipes are below the frost line, so why should they be affected by severe cold at the surface. When they dug it up, I could see that pipe was about 6 or 7 feet down.
The only thing I can think of, is that the fire hydrants are lifted by the frozen soil at the surface, and that stresses the pipes down below.