Can I just cover PVC pipes with elbows with soil underground?
Add loose soil then carefully compact next to and under the pipes. Repeat until you have compacted soil fully supporting the pipes from underneath. Then add soil in batches compacting each batch with your feet or with  a manual compactor plate on a shaft.
The purpose of this procedure is to avoid leaving uncompacted soil underneath and beside  the pipes. Uncompacted soil below or even on the same level as the pipes would compact over time and exert a bending moment on the pipes which could cause a break. Uncompacted soil above the pipes will eventually compact but will not stress the pipes.