Soil Bearing Test

[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!

 

[oldestguy]

Sounds like some form of local experience and relating that to density. I have used what we called the "T-bar" test. Nothing more than a 1/2" rod fitted with a handle making it look like a T. All it was used for was to rough estimate the density, between loose and hard. Since the recommended bearing had been determined from regular test borings, this was only used to see if the exposed site matched with the boring report. This was more sophisticated than the "heel test" and main use was when testing compacted fill for density, it was a quick test to check for uniformity in an area and where representative field density tests then would be made for the percent compaction determination.

There is a cone penetrometer test, done about like you describe, but I have never used that. Again takes some general rough interpretation of results.

 

[GeoPaveTraffic]

The name is a dynamic cone penetrometer.

Mike Lambert

 

[Deadblow]

Thanks! Yup, dynamic cone penetrometer was what I was referring to. I had also posted this question in the structural section.

 

[BUGGAR]

Geotech's are always saying we need more CPT's (for cone penetrometer tests). Owners call them CPT'$

 

[fattdad]

I'm not a fan of the DCP for evaluating bearing capacity. There is a much more prominent need to do proper geotechnical engineering in support of design and in advance of construction. The DCP will alert the field staff of unsuitable materials within a couple of feet. But for a 4 or 5 ft wide strip footing are you going to advance the DCP to depths of 8 or 10 ft? Are you going to use the DCP data to trump the geotechnical report signed by an engineer and used for design of foundations? I wouldn't.

So, sure it's a tool, just like a number 5 rebar. It's not some, "Certifying" agent to confirm bearing capacity though. At least not for me. . .

f-d

ípapß gordo ainÆt no madre flaca!

 

[newa]

Fattdad,

I agree what you are saying however, the designer like to stick note to the construction drawing like "qualified geotechnical engineer to verify the allowable bearing pressure at the foundation".
What we do in such situation is to ask the client to provide us geotechnical report previously carried out for the site. Then we inspect the prepared foundation visually for any anomaly with respect to the report. Then carry out number of DCPs as far as we can go. We carry out proof rolling test if possible to identify any soft spots immediately under the proposed footing slab. Then based on these observations we will verify or fail the prepared foundation. The DCP is not the reliable tool but at least it will tell you roughly what the ground is like. At the end of the day the ground will not change significantly under in the deeper depth compare to the geotechnical report. The only changes can happen in top couple of metres due to possible cut and fill or disturbances and DCP can give you some indications of the top 1 o 2m of soil.

So, rather than doing nothing, DCP can be helpful in such situations.

Looking forward to see some comments

Regards

Newa

 

[aeoliantexan]

I think it was the Burmeister penetrometer. I have see it used for that purpose in Detroit.

 

[geomane]

Attached is the DCP we use in my office. 15 pound hammer with a 20 inch drop. We occasionally use it in the field to inspect the soils at and below the foundation bearing level and compare to the geo report.