ICF Foundation in New Residential Bldg

[123gofast]

Greetings,

I'm just starting to build a house (my contractor is, at least). Today they poured the footings for the walls. I haven't been to the site to verify things, but I have a sinking feeling that not only is the footing too shallow, but it's also too narrow.

I think he put in a 24" x 6" footing. However, based on our local snow load (3.1 kPa), and the fact that we're building with 6" thick ICF (single story), it looks like the footing needs to be somewhere between 20"-38" thick (plus allowances if there's masonry) per the attached image.

There has been no geotechnical investigation at the site. It's a new neighborhood development and the area is known to have glacial till. Additionally, locally, there are many hoodoos that are sometimes near-vertical and 40ft+ tall with this same soil. It's puzzling to me because I it seems like a granular material littered with round boulders, but somehow there is some kind of adhesion (

https://www.zenseekers.com/story/ktunaxa-creation-hoodoo-views-land-eagle).

Anyway, I'm trying to gauge what the allowable bearing pressure should be. I don't have any equipment with me, but believe I could fashion up a T-bar using some rebar. It won't be the standard fancy one you buy from a shop, but should be close enough. Could someone provide me with a guide for depth of penetration and approximate bearing pressure? I know I had one a few years ago at my former company, but my brain no longer works so I need help.

If I can get gauge on whether this is 3000psf material, then I will feel a little better. I will need to verify the assumptions used in the ICFMA manual for concrete strength. If I can prove that what was cast on site is higher strength than what's assumed in the manual, then maybe I can justify the thinner footing.

I knew I should've gone to the site beforehand...

 

[EireChch]

My gut said width is ok but thickness is way way way too thin. I would have expected at least 12 inches (i.e. 300mm approx.)

I did a quick check for what the minimum is in the UK and it appears a minimum of 600mm wide by minimum of 150mm thick.

I have inspected many foundations before concreting to check depth, exposed subgrade etc and have never seen a 150mm thick, but seems like its permitted in good ground.

Glacial till either granular or cohesive should give you 3000psf if in fact that it is glacial till that has a high over consolidation ratio.

I think any homemade T bar or DCP is going to be very crude and likely of little use.

Your best bet is to:

1 - phone a geotech in the area and see if they allow you to pick their brain for free. Maybe theyll say " oh yearh i know that area, that ground is very good 3000psf for definite". This obviously comes with no liability.

2 - Employ a geo for maybe 500-750USD (guessing US market) to do a quick inspection, dcp and provide a one page letter.