High compaction high fine glacial till

[SteveNNY]

I am working QC @ Ft. Drum NY building shallow footing frost protected foundations housing & associated roadways. The site is glacial till, with high compactability and some pumping problems.(in some places as much as 80% fines with little rock, to boney material that needs to be broken up with a hoe ram). We have 2 & 3 roller compacted sand lifts on most of the pads & they seem to be working well, (No pumping) but some are true cut. I watched a Lull pump the soil quite badly on one of the proposed true cut pads.

I am concerned with the true cuts & the fine content plus the propensity of the fines to collect & hold moisture,(frost heave if the housing loses heat input during winter).

I found the discussion with breezeear -very soft soil but high relative compaction?- informative.

 

[CETech]

"Frost protected" footings with 80% fines? Here in Alaska structural fill is usually limited to less than 3% of 0.02mm to reduce the risk of frost jacking. Fine grain soils such as CH,CL,ML have the ablility to retain a lot of moisture and can swell considerably even without freezing.

 

[egmlca]

This may seem more expense in the short term, but considering the circumstances it would seem like a better idea to undercut the pads and replace the removed material with an import granular soil. CEtech is correct in that real fine grain soils will retain moisture which can cause heave during freeze cycles.