Problems with Lightweight Fill?

[RJ62]

It's standard practice here to not use a soil as backfill if its max dry density is below 98 pcf. The soil is usually an ML. LL and PI are not an issue but the ML is not used as backfill for footings, structural walls, or building pads backfill/fill.

My question is that no one has been able to explain why. Does anyone have knowledge, experience, or references as to the problems with using an ML/CL with a max dry density of less than 98 pcf as backfill/fill?

Is there a definite low point cutoff? 90 pcf, 85?

Thanks for any help.

Jefferys

 

[BigH]

Jefferys - putting a maximum dry density requirement for fill without consideration of other factors (specific gravity, etc) is not correct, in my view - but it is done in the Indian Highways specifications but with the caveat that the Engineer can make adjustments based on available soils. If we had followed it, we could not have used a sand for our embankment nor could we have used fly ash. For rationale(?), it is probably to ensure the the level of organics is low. I put a question to this several years ago - might want to do a search for it.