sand fill

[sandman1]

Local contractors have been using sand ( creek sand ) for fill in slab foundations. They tell me sand is self compacting especially if you wet it down. On my home the sand will serve to hold the concrete floor only and no load bearing walls or point loads. Is the above true or is there somthing I need to know?

 

[sc]

In the area where I live builders use what is refered to as slab loam. This material is a clayey silty sand that when wet to the point of stauration and allowed to partially dry will self compact to a level suitable to build on. In other areas pure beach sand is used with similar results. I would recommend this method for shallow fills only (less than 500mm, placed in 2 layers).

If you are unsure, let the contractor use it and then check it yourself prior to the slab being placed. If you are not happy at this point discuss it with the contractor.

regards

sc

 

[Ron]

Sandman1...
Sand is not "self-compacting" just by wetting it down. I follows a moisture-density relationship just like other soils. Granted, it often requires less compactive effort to achieve adequate compaction, but it almost always requires some effort.

Make sure the contractor compacts the sand fill prior to building on it. A few "in-place density" tests would be in order as well. Your contractor will "buck" this one, since it costs a bit of money. Total, assuming a single soil type, for both the laboratory and field testing for a single residence would typically be about $300.

 

[boo1]

I agree with Ron. Sand is not self compacting. All fill material must be put in lifts of 6-8 inches with compaction at each stage. (you cannot dump 2 or 3 feet of fill and expect compaction) Typically with residential foundations a small tractor with a back blade is used to install and compact the lifts. The final layer is leveled to grade a compacted with a vibrating tamp.

The "in-place density" tests Ron discusses is actually use to determine Building Code requiements (commonly 95% Procter). The test cost I pay are ~$200 each.