Scoria to protect pressured PVC pool pipe

[Pink Flamingo]

Our soil is clay and has moved significantly over the 40 year life of the pool. This caused a leak on two of the PVC pipes. Recently ripped all the concrete covering the pipes up and replaced the PVC. I am asking what the best and most suitable material is to fill in the trenches where the PVC piping sits. Currently purchased 20mm scoria which I am worried might be too thick? Should I go for something in the 5-7mm range? My main concern is putting pressure on the pipes and having another leak. Only foot traffic on top so no vehicular access needed. Thanks

 

[oz-plumber]

You could bed the pipes in sand also.
5 to 7 mm range is what we bed our pipes in
We call it '1/4 minus'