Settling, without compaction 1

[LHA]

I want to convert a sediment trap into a rain garden. I need to fill in 0.8 feet; 0.4 with sand, then 0.4' with topsoil. I don't care whether the sand and soil are mixed.

It can't be mechanically compacted, but to be landscaped and allowed to settle to a final depth.

How deep should each layer be placed to settle to a total of 0.8'?

A reference would also be appreciated (I'm not a geotech, but I have access to soem common texts).


Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve

 

[TDAA]

I think you are being overly concerned on the settlement of a surficial layer that is less than 1 foot deep, that is of nonstructiral use.

I would assume that if the area is large enough that the material would be placed using a dozer. Itf the material is placed with LGP equipment you should not see excessive compaction of the material at the time of placement. Also, the equipment should provide sufficiant compaction (in the range of 85-90% of a standard proctor) to limit excessive settlment. The materials should be close to the optimum moisture at the time of placement.

Since you are looking for 0.4' (~5-inch) layers, and I would assume you have some tollerance (slightly thicker), I would have the contractor place the material with no additional compaction to 5 to 6-inch lifts. A full 1' would allow for up to 20% settlment, which I doubt you would exceed if the materials are placed as noted above.

The only reference I can provide is my many years of fill observation and testing.