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How to intrepretate the penetrograph of soil penetration resistance

gadderrao (Civil/Environmental) (OP)
29 Jul 09 9:13
In our project we are adopting penetration resistance using base surface cone for measuring in situ compaction of soil. During the test instrument records the resistance of soil in a graph. Can any one help me about how to intrepretate the results of penetrograph to arrive the in situ compaction of the soil.  
KVgeo (Geotechnical)
29 Jul 09 11:05
gadderrao,

I am not sure I have ever heard of a penetrograph. Is it like a Dynamic Cone Penetrometer (DCP) or a McIntosh Probe?

In Perth, Western Australia, compaction testing for large sand fill projects is usually done with a DCP. Reference penetration values are usually established with nuclear densometer and compaction testing at the start of the job. The correlations are usually very reasonable.

In my experience DCP testing in clays is usually too variable to be of use.

Hope this helps.

KV  
dgillette (Geotechnical)
29 Jul 09 11:08
Not familiar with this test for compaction control, and it is certainly not common in US practice or literature - please describe it for us.  It is well established, however, by both formal research and the common sense of any laborer with a shovel, that penetration resistance is dependent on both density and water content, with very small variations in water content making large differences in penetration resistance.

Why not a nuke gauge or a sand cone?  They are much more direct indications of density, and are easy to interpret.  I don't like to use test methods that I don't understand.
KVgeo (Geotechnical)
29 Jul 09 11:57
dgillete,

AS (Australian Standard) 3798 - Guidelines on Earthworks for Commercial and Residential Developments - Section 7.2, allows for indirect in situ testing methods to assess in place dry density.

In direct methods include penetrometer testing as specified in AS 1289.6.3.2 and require some calibration with a direct in situ testing method (sand replacement, nuke testing, etc..)

In general practice the penetrometer testing is performed in association with moisture content testing to infer a in place field density in sand soils.

Aside from dry collapse issues, sand is a much more forgiving material than clay and silts and penetrometer testing is usually considered acceptable by design engineers for residential and light commercial sand fill projects in Perth.

And it's not a surprise its not common practice in the US. You guys are usually behind ;P.

KV
 
dgillette (Geotechnical)
29 Jul 09 12:21
Sounds like you wouldn't want to use it for anything but fairly clean sands - does AS 3798 Section 7.2 include limitations on what materials it can be used with?  With a lot of fines, it would be very sensitive to small variations in moisture, and it would be vulnerable to gravel interference unless the diameter is quite large.  Is it so much quicker and easier than a nuke gauge that it's worth having the less-direct method (which apparently requires material-specific calibration)?  The other question is why one would select a test method, and THEN go try to learn how to interpret it.

Are you working the night shift in Oz sleeping2, or are you in this hemisphere?
KVgeo (Geotechnical)
29 Jul 09 13:08
The benefit of using the DCP is that the test is usually performed after about a metre and a half of fill placement.

The fill is usually placed in accordance with a method specification which is determined at the start of the job by trial runs and nuke testing. The DCP is used for production quality control during the filling works.

These projects are relatively large and usually involve several metres of fill. The sand materials in the Perth region of Western Australia are typically fairly clean.

For clays and other materials nuke testing is usually the method of choice for assessing field densities.

gadderrao, I hope this helps. There is precendent for using penetrometer testing for compaction control, but I would only recommend it for fairly clean and uniform sand fills. Anything else stick to densometers.

Dgillette, born and raised in Oz now I live and work in Canada. Just like home only wetter, colder and completely different.
BigH (Geotechnical)
29 Jul 09 21:19
I'm aware that some areas of the world use dynamic cone pentration tests for compaction control - as dgillette says and confirmed by our transplanted Aussie, the materials used for fill should be such that the probe will penetrate - certainly wouldn't want to use it on a rockfill site - or a site using crushed 50mm minus stone.
dgillette (Geotechnical)
30 Jul 09 10:50
KVgeo - At least it's almost the same language, except in Quebec, eh?

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