Pocket Penetrometers 2

[theclipper]

I've been out of the soil testing end of the business for about 10 years and I was just sent a report to review that had site info based on these tools...what are your guys' thoughts on Pocket Pentetrometers?

Where would you be comfortable and not comfortable using them?

thanks,

 

[PSlem]

I was underpinning a house where the homeowner had hired an engineer to test. As he went around the house with his pocket penetrometer I kept telling him there was a trash pit. You are not going to get the big picture with one. I think every engineer should have as a minimum of equipment a DCP or something similar capable of testing 5' deep.

The optimist sees the glass as half full. The pessimist sees the glass as half empty. The engineer see the glass as too big.

 

[Panars]

I have used a hand penetrometer pretty frequently to determine the consistency of clayey soils (i.e. very soft to hard). I think it is a better tool than relying solely on SPT blow counts. That being said, it is not very accurate, and although I have used it myself I would be cautious of relying on hand penetrometer tests performed by someone I didn't know. There can be lot of variability in the results depending on how it is performed. Some things that can easily screw up the results are pushing on a piece of gravel, not pushing on a smooth surface, forgetting to reset the ring indicator, etc. And as you point out PSlem, it "tests" only a very small volume of soil. You have to use a lot of engineering judgement in interpreting the results.

 

[jakin]

I use it routinely as backup for split spoon or shelby tube samples of clayey soils that I am very familiar with. I would however not rely on it for soft to very soft clays, for which I probably would depend on in-situ vane shear test results. Its results are reliable when the sandy or silty content is not significant.

 

[BigH]

It is a tool - a primitive tool, but a tool. A piezocone is tool - a sophisticated too - but a tool. All tools have inherent advantages and disadvantages. But, in using the tool, you need to be aware of the limitations. I use the pocket penetrometer. I use the torvane. Are they my first choice? No. But at times they are used out of necessity for the lack of anything better being available at that particular time and place - and, it is better than jamming your thumb into the soil and trying to estimate consistency. No, but, given a situation, understanding the qualitative needs I have and using judgment, they can be useful. Judgment is the key.

 

[Dirtguy4587]

Excellent comment BigH. All tools have a use and an application...It is the engineers judgment that defines the value of the information the tool gives.

In my own experience, I typically only use the pocket pen for field characterization during exploration...and rely on the other more robust techniques for actual design.

 

[jdonville]

theclipper,

As others have said, a tool - and one of many.

I will generally ask that PP readings be made on cohesive split-spoon/shelby tube samples. Constant-strain tests are performed on selected SS and usually all ST samples in order to provide corroboration of the PP UCS values for samples that are not assigned constant-strain testing.

As has been stated before, it is a crude tool and should be treated as such. Soft materials should be subjected to more sensitive field and/or laboratory testing where appropriate.

Jeff

Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com