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Correlation between modulus of subgrade reaction and DCP or CBR

DOD (Geotechnical) (OP)
2 Sep 02 14:49
I need to know if there is a correlation, a formula or any method to determine the modulus of subgrade reaction using the DCP index or CBR values. I want to evaluate de CBR and modulus of subgrade reation of sois using only DCP index, for airfield pavement evaluation.

Thank you for your replies
Abedkayrouz (Materials)
3 Sep 02 10:05
Dear Daniel,
To correlate the DCP with CBR you may use the book M.Y. Shahin (1994) “Pavement management for airports, roads, and parking lots”. Chapman and Hall
And to correlate the CBR with subgrade modulus uses the book Croney D, & Croney P. (1991). “The design and performance of road pavements. (2nd edition) Mc Graw-Hill Book Company.
Other researches have correlated CBR with DCP and Subgrade modulus like US corps of Engineer. Harison J.A. Australian Road research
Abed El-Kader Kayrouz
Please send me notification if you received this emails.
DOD (Geotechnical) (OP)
4 Sep 02 13:49
DOD (Geotechnical) Sep 4, 2002
Dear Abedkayrouz,
Thank you for your reply, I found it very usefull. I already have the correlation of the US corps of engineer between DCP and CBR values, but I don`t found anything about CBR or DCP with subgrade modulus. I will try to find those books you recomended but it would be very difficult for me because I live in Paraguay in South America. If you have those books i`ll apreciate if you could send me by mail or in this forum the information about the subjetc.
My mail is
Sorry for my english.

Thank you for all.  
Focht3 (Geotechnical)
25 Sep 02 15:18
Why do you need modulus of subgrade reaction?  What are you designing?
bartshippee (Geotechnical)
1 Oct 02 11:18
Along the same line, I'm looking for a correlation between SPT values and Resilient Modulus.  Perhaps a correlation from SPT to CBR, then Mr=1200XCBR (or Mr=1500XCBR)?
pigdog (Geotechnical)
7 Oct 02 9:45
If you need books, try, or  Both of these are great sites for used books.
Focht3 (Geotechnical)
7 Oct 02 13:01
Dynamic Cone Penetrometer (DCP) is a very poor tool for evaluating modulus of subgrade reaction (k) or modulus of rupture (MR).  In my opinion, you would be better off guessing - at least then you would be applying your judgement to the problem.

If the airfield exists, get the airport management to give you a count of take-offs by aircraft type per year.  [Take-offs cause the majority of damage - not landings.  This is counter-intuitive but true.]  You will also need annual condition surveys (if they exist) to evaluate pavement deterioration over time.  Back-figure the (k) or (MR) using the loading, structure properties and pavement life.  You will get a much better answer this way.

You can use DCP to find weak areas that may need to be replaced (and not left under your new pavement.)
bartshippee (Geotechnical)
7 Oct 02 13:31
Sound advice for DCP, although I'd feel better makng a guess while I'm looking at the DCP data rather than a blind guess.  I'm interested in a different MR, Resilient Modulus - not modulus of rupture.  AASHTO uses it in their pavement design procedure.  The actual test procedure is so elaborate that few testing labs run it.  The setup costs a fortune.  PennDOT, recognizing this, allows for alternate design procedures, depending on importance.  For a low impact project, one does not need to do laboratory testing (MR or CBR).  This is where I am confused.  To do an AASHTO pavement design, you still NEED a soil stiffness measure.  We have the ability to split-spoon the subgrade through our 4" diameter pavement core hole.  I'm wondering how to get from SPT values to MR values without lab testing.  Any suggestions?
Focht3 (Geotechnical)
23 Apr 03 16:13

Sorry for the late reply; somehow I didn't 'see' your question until a few minutes ago.

You're right - MR - is resilient modulus in pavement design.  I goofed - guess it was late when I wrote that response -

About the resilient modulus test procedure: too bad AASHTO chose such a tedious test to use in pavement design.  Seems to me they 'fine tuned a coarse knob.'  Oh, well - maybe with the next design guideline iteration...

If you feel the need to run DCP, then go ahead - some data is better than none.  But use it to compare areas, not provide design parameters.  Soil stiffness affects penetration resistance, but the DCP values are not a measure of stiffness.  For me, field CBRs or plate load tests do a better job of measuring the in situ soil stiffness.  (Some of you who read this may note that this is the first time I've recommended the PLT!)

BigH (Geotechnical)
23 Apr 03 16:45
Remember that field CBR values or PLTs are under "current conditions" - these may change say from dry to monsoon seasons, etc.  So - be careful with correlations of DCP to CBR (I am assuming that you are using the TRRL miniature DCP apparatus - where, by the way, I see some correlating these blow counts to double digit decimals for the CBR!!! - caution:  be practical). Most designers will use soaked CBR values - taking into account to a degree "monsoon" periods.
Focht3 (Geotechnical)
23 Apr 03 18:47
BigH is right, of course.  Perhaps I was too hasty in "recommending" CBR or PLT.  (Nah - I was clearly talking about "in situ" conditions.)  It is very important to take into account the "soaked" conditions when designing pavements.  Field tests - including DCP, SPT, field CBR, PLT, DMT, pressuremeter - may or may not test the "worst case" conditions that are most appropriate for design.

By the way, there is a Road and Highway Engineering forum - the link is at the bottom of this posting.  It's a good place to post these kinds of questions.


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