Perhaps there is no definite answer but... what is your favorite trench fill around drain lines under a concrete slab?
I know that in some places the native soil is just right. I know some like sand because it protects the pvc from rock abrasion. I know some don't like sand for drainage or compaction issues maybe affecting the slab itself and because it can move the pipes during compaction. I know some like 3/8 crushed rock because it compacts well and keeps the slab happy... and some who'd think that is crazy. I know that some folks would only put cast iron under a slab, but I'm not one of them.
I have a drain system going in on a well drained heterogeneous sand/gravel/cobble river terrace and my options are to use the sandy fines from the native soil (no clay to speak of in it), bring in some sand, or bring in some gravel (crushed , or some combination of it all. It is a small system, so cost not much of a concern with any of these materials. Out of municipal jurisdiction... state code is UPC and the inspector is about a hundred miles away and doesn't return calls.
Unless someone can convince me otherwise, I'm bringing in some sand for directly around the pipes for a few inches or so... wetted and tamped before filling with the native soil (minus the big cobbles) for a while further until I get to my subslab crushed gravel.
I know that in some places the native soil is just right. I know some like sand because it protects the pvc from rock abrasion. I know some don't like sand for drainage or compaction issues maybe affecting the slab itself and because it can move the pipes during compaction. I know some like 3/8 crushed rock because it compacts well and keeps the slab happy... and some who'd think that is crazy. I know that some folks would only put cast iron under a slab, but I'm not one of them.
I have a drain system going in on a well drained heterogeneous sand/gravel/cobble river terrace and my options are to use the sandy fines from the native soil (no clay to speak of in it), bring in some sand, or bring in some gravel (crushed , or some combination of it all. It is a small system, so cost not much of a concern with any of these materials. Out of municipal jurisdiction... state code is UPC and the inspector is about a hundred miles away and doesn't return calls.
Unless someone can convince me otherwise, I'm bringing in some sand for directly around the pipes for a few inches or so... wetted and tamped before filling with the native soil (minus the big cobbles) for a while further until I get to my subslab crushed gravel.
