A. Irrigation lines are typically installed at a depth of 10”(to the top of the pipe) to prevent a standard 8" shovel blade from reaching the lines. A 12” depth would be best. This is for residential installations, not commercial. The mainline (pressurized line) should be between 12” to 18” deep. This is well below a shovels depth. Here's an expert tip: at the transition point between planter and grass areas, cover the pipe with wood then a flat rock. That way, they get hit before the pipe or any wires when digging. I hope this helps.
Lorne Haveruk, CWCM-L, CID, CIC, CGIA, CLIA, WCP
DH Water Management