DCP to SPT

[moe333]

Hi guys,

Trying to correlate DCP data to SPT. I have searched the threads and found some information, but nothing that quite answers my questions.
The DCP is from Humboldt. It has a 17.6 pound hammer, a 20 mm (0.8 inch) diameter, 60° cone, and a drop height of 575 mm (23 inches).

https://www.humboldtmfg.com/dual-mass-dcp-threaded-ends.html

I found a reference from the Minnesota Department of Transportation that has a correlation from DCP index (DPI) (blows/mm) to SPT. Pages from this reference are attached.

http://www.dot.state.mn.us/materials/researchdocs/User_Guide.pdf

Here is the correlation:

log DPI = -1.05 + 2.03 log SPT

According to this reference, the log of the DPI is directly proportional to the log of the SPT. This doesn’t make sense to me since lower DPI should result in higher SPT. I must be missing something. Perhaps the SPT in the equation is feet per blows rather than blows per foot?

Does anyone have experience with this correlation, or can recommend a different correlation?

Thanks

 

[moe333]

Forgot to mention, my data is for stiff clay. There are probably different correlations for clay versus sand.

 

[moe333]

Correction… DPI is mm/blow

 

[Ron]

moe333....sounds like a Sowers DCP. Look up Sowers and Hedges in ASTM STP 399. If I can find in my files, I'll post the table for similar soil type.

 

[BigH]

I've not used the Sowers equipment (I've confirmed that you have it - see third reference below which also gives correlations - 100+ page report by Minnesota DOH).

As we have seen in many threads, there are many DCP tests being used. For sake of completeness, I have included a few of the probes that are used extensively in SE Asia (the JKR Probe (Malaysia) and the Mackintosh Probe). Somewhat similar except for the drop and hammer weight. There is also the Clegg hammer and the TRRL dynamic cone. They all have correlations to the SPT, etc. See the second reference (gnpgeo). My personal use of dynamic cone testing was the Canadian "Pentest" which was a 60deg cone, 50 mm diameter using the standard penetration test 140# hammer dropping 30 inches. This was the test of choice for our investigations although we had a "hand" tester using the same equipment but a 50# hammer.

Sorry - can't help exactly with your issue but thought that these other references might be useful. A suggestion that I am sure you are considering, etc. is to develop your own correlations - as many correlations are not only equipment issues but also location related.

http://parsgp.com/edu/edu19.pdf

- Mackintosh Probe Test 7.98 kg hammer dropping 300 mm (very popular in Asia, especially Malaysia)

http://www.gnpgeo.com.my/download/publication/l2009_04.pdf

good intro to various in situ testing - discusses JKR Probe - which sounds like yours but only 280 mm drop.

https://www.google.com/url?sa=t&rct...Aj4Kzo6PUAhWENY8KHey8BicQFggzMAM&url=https://

http://www.researchgate.net/file.Po...5raq3ZR80ep-g8aEw&sig2=WgmCnEmXuNXhhwCg4737zA

- Sowers DCP