I'm very sorry to hear about your problem. I'm sure none of us want to have to address under ground broken pipe issues especially in the middle of winter. If it were me, I would try to find the builder and get their advice. If you don't know who built it, I'd call local builders and get their advice on how to proceed. I suggest calling more than one to see if you get different answers. The local guys should be familiar with local codes and conditions. One might have a clever approach, or they may all say the same thing, but then you'll have a realistic idea of what you are up against. Wish you the best.