House Pad - Soil Samples

[LSUengr2013]

Hey All,

I do not deal on the realm of geotechnical often (structural guy here) and I have a wonderful friend who is wanting to build a new home on some country property they have. They got a soils report done on two 6' borings where their house Pad will be located. The reports are attached below, their dirt guy is saying that they should dog out five feet down and bring back in proper fill. I know the PI values seem high but I would like a little more knowledgeable input as to whether that is required or if this dirt man is trying to pull one over on them. Any insights would be greatly appreciated!

 

[oldestguy]

This looks like a high-shrink- swell type clay that will change in volume with changing moisture content. I'd caution that no fast growing trees are ever planted near the house since that will make for lots of problems. Going deep with foundations or soil replacement tends to lessen the heaving and settling with moisture content changes. However, even that may still have heaves and settling depending on the seasons. I's go by what is common successful practice in your area. The soil replacement sounds very much needed.

 

[LSUengr2013]

Thanks for the insight, I was afraid of that. I suppose they could potentially go to a pier and beam design with some deep footings instead of grubbing and replacing the entire footprint of their home.

 

[dik]

Does the clay moisture content change very much... in Winnipeg, we have a highly plastic clay (nearly everywhere) and other than the top 1/2" the clay is saturated and the moisture content is very nearly the same... even in a dry year. Our plastic clays really 'lock' the moisture in.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[LSUengr2013]

This is in the Southern US, Louisiana more exactly, I believe our water levels tend to fluctuate greatly down here. But like I said I am no geotech haha.

 

[theCorkster]

High moisture contents suggest low density, likely moderately to highly expansive clays. Run Expansion Index test to get better handle on expansion potential. Worked in areas of highly expansive clays (desiccation cracks 2 to 3 inches wide, 3 feet deep); over-excavation to 3 feet beneath finished soil grade and replacement with non to low-expansion potential fill to 5 feet beyond structure including exterior flatwork seems to be working well since the mid 90s.

 

[oldestguy]

In Wisconsin I've seen significant moisture (and volume) changes down as deep as 10 feet. Depends on the season and of course high plasticity clays.