Test to Determine Soil Bearing Capacity

[Deadblow]

Hello All,

I am starting my career as an EIT (mostly structural) but I worked as a carpenter for 10 years. I know when I used to pour wall footings, a testing agency would send a guy out with a steel rod and like a 35-45 pound weight which impacted that rod from a very specific height. He counted the number of blows and that was then used to determine the allowable soil bearing capacity. What is the name of that test? I thought the guys in the field called it a niece-bar test (spelling?), but I can't find any such test on the internet.

Thanks for your help!

 

[BadgerPE]

Sounds like a dynamic cone penetrometer test, or something similar. The guys that perform these tests often have some slang name for the test that doesn't match up with the technical name for the test.

Dynamic Cone Penetrometer

 

[sbisteel]

Sounds like a standard penetration test to me? (SPT)

 

[Deadblow]

Yeah, I think the SPT but on a small scale. The weight was lifted by hand and there is no way that it weighed 140 lbs. Is the SPT allowed to be extrapolated from a smaller version (man-portable) of it? I guess I got their slang for the test.

 

[sponton]

yeah second that, Standard Penetration Test (SPT)

 

[hokie66]

No, what the OP described is not the SPT. As BadgerPE said, it is some type of portable penetrometer, and these are correlated to attempt to mimic the SPT.

 

[oldestguy]

Duplicate posts are not desired here. In the other post I described my experience with a rod penetrometer.

 

[Ron]

What the OP described is a dynamic cone penetrometer test, also known as the Sowers DCP after George Sowers, who developed the method and its initial correlations.

 

[darthsoilsguy2]

These things have different names in the field.... but Dynamic Cone Penetrometer is definitely one of them. if google image it you'll see what they look like brand new before the abuse starts. most of the kits are sold with a hand auger and auger rod extensions so it only half the package. just a little FYI on tech language since you sound like you might work with them. The DCP is not for "determining" allowable soil bearing capacity. It is for confirming base assumptions of soil bearing capacity as developed and reported in the geotech study by drill rig (or test pits) and by a licensed geologist/geotech-egr. Or it is for confirming foundation bearing assumptions based on qualitative information on soils including material type and subgrade proofroll/compaction testing/fill materials/fill placement observations for foundations bearing on fill... or assumed low bearing pressure based on soil type and local geology for cut sites that are confirmed to be original undisturbed earth. also fyi the vast majority of home construction do not have a geotech study in the building pad. there are papers out there for correlation of this equipment to bearing capacity, but it really should be considered more of a double check, and double checks are good. The blow counts are only half the info, a qualitative description of each layer of soil tested in the hole is important in DCP testing.

There are occasions where a geotech study will use these devices but generally as a last resort due to limited access or on projects that don't have much load... but if done in a geotech study that would have occurred well before your presence on the site as a contractor

 

[Deadblow]

Ok, thanks! Yeah, I looked at it on google images and that is definitely the device I was referring to. @darthsoilsguy2, wow thanks for such a detailed response! I appreciate it.

 

[XR250]

Speaking of DCP tests. Had a job recently where the client wanted to add a second story to and old house. I probed the soil adjacent to the existing footing and my rod was easily pushed 18" below the footing with one hand. Had the contractor bring a geotech out. His DCP test yielded an allowable bearing 3000 psf. Don't see how this is possible, but
he stood behind it so that is what I ran with on my design. Fortunately, my loads were only in the 750 psf range so I did not lose too much sleep.