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jpyeron (Electrical)
22 Jun 10 5:51
Can someone recommend a penetrometer for a one time use?

I found one for 60$ at Amazon.com.

 
PEinc (Geotechnical)
6 Jul 10 21:26
Make sure that the penetrometer you buy has an attachable/removable, larger diameter foot so that you can use the penetrometer in softer soils.

www.PeirceEngineering.com

jpyeron (Electrical)
6 Jul 10 23:28
Then this

http://www.grainger.com/Grainger/items/5DPJ8?cm_mmc=Google%20Base-_-Test%20Instruments-_-Soil%20Testing-_-5DPJ8

and its adapter foot should do the trick.

This does beg the question why use a dial penetrometer (600$) or a cone penetometer (1300$) or even a dual mass dynamic penetrometer (3000$)

http://www.grainger.com/Grainger/soil-testing-penetrometers/soil-testing/test-instruments/ecatalog/N-csc?op=search&sst=subset
 
GeoPaveTraffic (Geotechnical)
8 Jul 10 16:45
Some of those other penetormeters test a larger volume of soil.   
Helpful Member!  oldestguy (Geotechnical)
8 Jul 10 19:48
For a single time use I would not use a penetrometer.

Instead get a cylindrical sample and test it for unconfined compression strength.

How?

Well take a tin can or similar metal cylinder  (both ends open) and force it into your material to test, perhaps with some excavation around the sides to assist in the penetration. Ideally the undisturbed length should be twice the diameter.

Then take it home to your bathroom scale and slowly compress it.  At a deflection of say 10 to 20 percent of the height, use that poundage to figure tons per square foot.  It will be a rough figure, but probably more accurate than a penetrometer anyhow.  Cost is zero.

For many tests, extrude the sample out on the job and wrap in plastic to maintain moisture.   Oh yes, take the bathroom scale out there if the wife OK's it.
PEinc (Geotechnical)
8 Jul 10 20:27
Is there an ASTM number for the "Tin Can Test?"
I bought a penetrometer for a "one time use" and have used it many times over 20 years.  It was cheaper than 20 years' worth of soup cans and, when using it, I look a little bit more professional than if I were to use a tin can and a bathroom scale.

www.PeirceEngineering.com

oldestguy (Geotechnical)
9 Jul 10 21:55
Hey Pierce, we gotta have some fun here.

When I first went on my own, without any test equipment, and not much money, I used a drill press and a bathroom scale for testing split spoon samples for Qu.  It worked and later the more fancy stuff was not any more accurate.

I suppose out on a job where you need to create an impression that you are an expert, this tin can thing might not be so hot.  Then again, real experts may criticize the pocket pen and ask for a more sophisticated test method as being more dependable.  Depends on what the result is used for.
 
PEinc (Geotechnical)
10 Jul 10 0:23
oldestguy, I agree.  I had a job recently where I had to design a cofferdam in the river where all could see were big rocks in the river bottom.  In addition, the adjacent historic structure appeared to be founded on bedrock projecting from the river.  There were no borings in the river.  The contractor was already on site.  I had him drive a pipe into the river bottom and extract it.  I had them cut the pipe open.  The ID of the pipe matched the diameter of a concrete cylinder.  I took the "undisturbed" sample from the pipe, put it into the cylinder, got its now moist weight, flooded the soil-filled cylinder, got its saturated weight, and then estimated its phi angle.

The project engineer questioned my use of this non-ASTM testing method.  I told him that, since he didn't do any borings in the river, my method gave better information than he had.  I also told him that I had better information than if he did have borings.  He backed off.  The cofferdam was built and performed as intended.  Sometimes you just gotta do what you gotta do - like your tin can experiment.

www.PeirceEngineering.com

PEinc (Geotechnical)
10 Jul 10 0:25
Oh, yeah.  I also used a bathroom scale.

www.PeirceEngineering.com

jpyeron (Electrical)
10 Jul 10 9:02
I think I am going to spend less than $100 in tools on this one. I like that there are other ways of doing it, but for me (I am an electrical engineer) they are more "complicated".

Thanks for everyone's help on this.
 
BigH (Geotechnical)
10 Jul 10 9:09
Basically I never "knew" ASTM tests for soils until I went overseas and in Laos - we always used Lambe and the "company" standards.  Served us quite well.  Here in Indonesia, I did a soil sieve for a consultant as a favour and their engineer got all upset because I didn't quote C31 (or whatever it is) - I got ticked off and told him it wasn't "aggregate" so I used the soils D version . . .  I understand the need for consistency but sometimes the names get in the way of the doing. oldestguy - loved your note . . .  I'll get back soon.  
geoman110 (Geotechnical)
12 Jul 10 21:14
"I took the "undisturbed" sample from the pipe, put it into the cylinder, got its now moist weight, flooded the soil-filled cylinder, got its saturated weight, and then estimated its phi angle"

PEinc, I am wondering what is the base/theory for estimating the friction angle by this method.  If the sample is below the river bed, it must be below the groundwater table anyway which means the in-situ condition is saturated.  In this case, the weight of a clayey sample before and after flooding it should not change that much.  In case of a sandy soil, it is a bit complicated as saturated sand may lose some water during sampling and extraction and then you get it back to saturation.  In this case, the weight difference may mean something.  However, it is complicated as you cannot say how much water the originally saturated sample may lose through the sampling process.  On the other hand, I can understand if you let the sample dry first then measure the dry weight and then make it saturated, and measure the saturated weight.  In this case, the weight difference for sandy soils provides a base for estimating the friction angle (may also applicable for clayey soil).  I appreciate if you can help me to understand your method.
 
PEinc (Geotechnical)
12 Jul 10 22:29
After the pipe was cut open, The very silty soil sample was very moist, probably still saturated.  Then I completely saturated it and got its total weight. I estimated a drained phi angle and ignored cohesion.  I'm not in my office now and can't remember the exact conditions because I work on several projects a week and this project was a year or two ago.  During construction, the soil behind and in front of the sheet piling was saturated.

www.PeirceEngineering.com

geoman110 (Geotechnical)
13 Jul 10 19:10
Thanks for the reply.  Unfortunately, I am still struggling to grasp the concept and appreciate a help.  As I stated before, if you dry up the sample in the cylinder (undisturbed condition), take the weight and then saturate it, take a weight again, that can provide a base to estimate the void ratio, leading to relative density, and then friction angle.  However, taking it from the very moist state to fully saturated, I am not sure how much information provides.

 
PEinc (Geotechnical)
13 Jul 10 20:45
You may be overestimating the importance of accuracy in soil properties for designing retaining wall under most conditions.  From my experience, the vast majority of sheeting walls are designed based on little or no tested soil properties.  Even major, national, design-build earth retention structure contractors rarely have useable test results for soil properties.  That's part of the "art" of soil mechanics where we often deal with layered, non-homogeneous soils.  Using a penetrometer or other non-standard test is still a step above just estimating soil properties from boring blow counts, sieve analyses, and Atterberg Limits which are about all we get on almost all projects.  Almost nobody spends money for useful soil tests.  

www.PeirceEngineering.com

oldestguy (Geotechnical)
14 Jul 10 16:49
Pierce tells us what results from engineers bidding on jobs and the fierce completion that is out there.
PEinc (Geotechnical)
15 Jul 10 10:13
I didn't bid the job.  The contractor hired me to design the cofferdam after the contractor was awarded and started the job.

If Engineers are going to provide a geotech or foundation report for a project, the report should have some useful information in it besides cut and paste geologic history.  Is it too much to ask for some actual unit weights, phi angles, and cohesion?

www.PeirceEngineering.com

PEinc (Geotechnical)
15 Jul 10 10:15
Sorry, oldestguy.  I misunderstood your last comment.  I agree with you.  Engineers are quoting on minimal scope in order to have the lowest price.  The owner gets what he pays for and the contractor gets nothing useable.

www.PeirceEngineering.com

geoman110 (Geotechnical)
15 Jul 10 23:54
I agree with you guys.  There are some engineers that devalue the geotechnical engineering which I believe is one of the most complicated and difficult branches of civil engineering

 

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