backfill

[EddieWalker]

Sand does not "self compact" when wetted. It will settle, but it won't compact.

Maybe I wasn't clear in my comments. When jetted, or saturated, sand will self compact enough to meet code in CA when installing water utility lines for cities. It was my job to jet the sand. When I put enough water into the trench, the water would force it to settle and become flat. Generally there was at least a foot of sand on all four sides of the pipes per code. For really large pipes, it was a little more, but not a lot. The inspector would measure the thickness of the sand after I had jetted it. When we failed, it was because there wasn't enough sand on top of the pipe because too much had settled.

After that, I would add water to the dirt that was put into the trench that was usually compacted with a jumping jack. When that was done, the inspector would test that for compaction. Most of the trenches where 4 feet deep and would get about 2 feet of sand and 2 feet of dirt. The only thing done to the sand was the jetting, which I was told self compacted from the water.

If you are saying that they inspectors and contractors I subbed for are wrong, then I'll take your word for it. I've always thought they where right from seeing how solid the sand became after adding all that water.

 

[orezok]

6mil poly, is not a "quality" vapor barrier. A good under slab VB would be a Steowrap or something similar.

A small spelling error, but I'm pretty sure you mean "Stegowrap". When I was building schools, the only vapor barrier specified was Stegowrap.

 

[Billrog]

Eddie jetting the sand would definitely have it fill all the voids around the pipe and settle it enough that the pipe would be stable and not pull apart from any future settling. I had to replace a 6" main that at some point someone had thought it would be a good idea to use hog fuel. After 10 years it settled so bad the joints were coming apart in places.

 

[Egon]

Consolidating sand using water does not give the same results as a properly compacted sand.

 

[EddieWalker]

Consolidating sand using water does not give the same results as a properly compacted sand.

How do you compact sand?

 

[Streetcar]

How do you compact sand?

I have used vibratory roller, as long as sand was at proper moisture content

 

[Egon]

How do you compact sand?

Proper water content. ( described in a previous post ). And a vibratory packer with smooth rollers or plate. Air on the go will also work.

There are places where water jetting sand in a trench is not allowed.

 

[Cord]

A small spelling error, but I'm pretty sure you mean "Stegowrap". When I was building schools, the only vapor barrier specified was Stegowrap.

You are absolutely correct. I will say the one project that I had move to litigation was specified as being built on a sand bed using Stego for the under slab vapor barrier. The contractor replaced the Stego with poly and placed it between the sand and crushed stone. When they installed the sand bed they did so by driving over the sand that had been previously installed. This compacted the sand and caused the stone to puncture the vapor barrier. With VB full of holes the sand now wicked the moisture up to the slab where is caused a host of flooring adhesive problems.