In each description I've seen for the installation of popup sprinklers, the pipe is being dug deep into the ground, below the lowest point of the sprinklers. I was thinking of making a pretty shallow trench - let's say enough to cover the pipe + 5cm. For each sprinkler I'd add a T, with a pipe going down and back into the sprinkler. Explained in ascii-art:
|x| sprinkler |x| |x| pipe -------^----
|x| pipe ----+-|x|---------- | |x| +--^
Main reasons: less ground to dig up / repair afterwards, easier access for the future maintenance. In terms of temperatures, we go down to maybe -1°C on a few nights in the winter, but otherwise nothing extreme.
I suspect there's a good reason why people don't do this - why is that?