Soils test for residential footings

[eng1234321]

For residential projects in my area, I often see soils test at footing elevation completed with Static Cone Penetrometers. I am wondering everyone's thoughts on this method for residential footings. Here is an example of a digital model of the equipment I am referring to:

https://www.humboldtmfg.com/digital-static-cone-penetrometer.html

 

[oldestguy]

An elaboration on the "T" probe. Still very approximate. However better than no site inspection.

 

[GeoEnvGuy]

My thoughts are why are you wasting time doing any testing for residential footings that built to code will have low bearing pressures just given the minimum width of the foundation to the total weight of the house.

 

[oldestguy]

Did a lot of these. Paid well. On a rare occasion found problems. Somehow contractors seem to feel it clears them from responsibility.

 

[Eric C.]

I do quite a few of these except I don't use a T-probe because I don't have one. A lot of the time I'll take a soil sample for a Proctor test and take a couple of nuclear gage readings. Mostly when the contractor is wanting to place the foundation in fill but not always. Like oldestguy, occasionally I find a problem that needs addressing and, again like oldestguy, I get paid pretty well for these jobs.

 

[geotechguy1]

I have used these. It looks fancier than a heel test or pushing a bit of rebar in but isn't much better. Doesn't really tell you much about the soil that's actually along a theoretical slip surface or within the zone of influence but then, houses are light and if it's got a full or half basement it doesn't matter anyway. Especially if you think about the 3d effects of the basement walls.

 

[Ron]

As OG notes, it is approximate. One method I've used in the past is to do a site specific correlation between the cone penetrometer and in place density tests. It works for certain soil types, but not for others (ok for coastal plains sands but misleading in "hardpan" and gravelly soils). When you do the correlation, you can then check a lot of areas in a short period of time.

Also as OG notes....better than no inspection