Amount/purpose of gravel around drain pipe

[KristenJensen]

Hello all,

I just had the under-slab plumbing completed at my 1951 Maryland home. Old CI pipe was removed to property line and replaced with PVC. Old Type M copper was replaced with type K to property line. Question is regarding gravel. I saw the plumbers placed gravel beneath the pipe about 1/3 the way up the pipe walls. I have a ton of 3/4" washed gravel coming in for french drain and adding more to this load would be a negligible cost.

What is the purpose of the gravel beneath the waste line, and if cost and labor were not a factor, how much gravel should I use and how should I pack it? The plumbing was already inspected and approved and its backfill time. Should I just add back the soil or should I increase the amount of gravel? I would keep enough room to fill 4" of concrete. Thanks and see picture below.

 

[James Henry]

He used the stones as a solid base. Sweep the stones off the top of the pipe and back fill with dirt.

 

[Sponsor]

 

[wwhitney]

What you want for backfill is easily compactable (or almost self-compacting) material without sharp edges that could damage the pipe. So round gravel would be fine. Sand would be fine. Non-rocky native soil is okay, albeit harder to compact. Crushed rock (sharp gravel) should be avoided.

Cheers, Wayne

 

[Jeff H Young]

Id use more gravel . I have used all native soil many times but this is better

 

[KristenJensen]

Thanks everyone. I decided to refill with native soil. Not great. Because of the high clay and water content, it doesnt compact easily. When I stomp on it, it buckles up in an adjacent area (like a water bed). If I could go back, I probably would have brought in sand by a truck and refilled. Now any casual reader/visitor with similar soil knows too.