It is a typical design for a civil site plan to pour some concrete around those elbows to absorb the inertia of the water hitting the turn. If you -really- want to protect -all- the PVC, you can encase all of it in concrete. That's usually only used on PVC that carries electrical or data cabling. So the guy on the backhoe installing a sprinkler system 20 years later doesn't dig through it.