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Foundation - SW-SM high water table

Foundation - SW-SM high water table

Foundation - SW-SM high water table

Hi there,
I am designing a home (1 storey, with an attic space loft facilitated by attic trusses) and the soil is classified as SW=SM. d10=0.072, d60=0.22, Cu=3.1, K=5.18E-03 cm/sec
I was initially told that the site was approved for a steel building to be build, with a slab on grade foundation. I began drawing the home, but upon further conversation with the owner, he revealed that the water table was very high (3'10" from surface) and he did not want to have to constantly pump water. He told me that he has excavated roughly 6 feet down and filled the site with 'a' gravel, compacted in small lifts. He has asked that I use a shallow frost protected insulated monolithic slab foundation. The proposed construction would be a 38x32 building, as described in my first sentence. The roof (to be designed by the truss manufacturer, is requested to use roughly 40% attic trusses, and the remaining 60% to be a vaulted or cathedral style, which would maintain the same roof lines as the rest of the roof. The site is in mid-northern Ontario, Canada. Snow load is ULS: 1.44kPa, 30.1psf, SLS: 1.3kPa, 27.1psf
I have several questions:
1. Using the information provided, would the soil be sufficient to bear a wood-framed building of no unusual design, on a monolithic shallow frost protected slab.
2. I have already begun working, under assumed site conditions, and it was then revealed to me that the conditions are not as initially described... what should I do?

RE: Foundation - SW-SM high water table

You could (a) auger a few holes to determine the soil type, (b) get a soil report or (c) run from the job. Your choice. I like (c).


RE: Foundation - SW-SM high water table

If the site has been excavated and well compacted Gran A has been placed to a depth of 6', you should have no difficulty in using a stiffened slab foundaton, with perimeter insulation extending the depth of frost penetration... I've done a few of them in mid-northern Ontario... not often relying on a geotech report, but a test pit dug with a backhoe.

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


RE: Foundation - SW-SM high water table

Thank you for the replies!
The soil report is where I got the soil classification from, it is SW-SM.
I feel a bit better about the ground, although i do wish he had put down some geotextile before he placed the gran a, for peace of mind.
Thanks again! I just found this forum, and I am very happy to see such prompt replies!

RE: Foundation - SW-SM high water table

With 6' of gran A and residential loads, there shouldn't be an issue.

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


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