I have to design a rigid pavement road and conduct geotechnical investigation along the road alignment. In this regard, I need to conduct a few California Bearing Ratio (CBR) tests along the road length. What is the requirement of CBR test frequency, namely, after how long distance, the test shall be repeated as per international standards such AASHTO or ASTM or so on?
Hi Dr. Ullah,
Interesting question, I found the following on TXDOT website,
http://onlinemanuals.txdot.gov/txdotmanuals/pdm/geotechincal_investigation_for_pavement_structures3.htm
"Frequency of sampling depends on the level of investigation, uniformity of soils, and the potential for detrimental reaction from chemical stabilization." General recommendations for various soil conditions are:
Uniform 0.5 to 1.0 mile
Non-uniform 0.25 to 0.5 mile
Highly variable 1,000 ft. to 0.25 mile
Potential sulfate bearing 500 ft.
I hope this will help you,
Regards,
Michael
Thanks Michael,
your literature is very helpful. I was planning to conduct CBR at 400 m. But now I shall change my strategy and conduct CBR at 800 m for uniform strata and 400 m for non-uniform one.
It depends on many factors related to the soil nature and uniformity, however, for uniform soils I would recommend a sampling distance of 1km along the axe of the road.
Dear Ahmad,
Thanks for your reply. If the length of road is very short such as 2 km, what shall be the sampling distance? One thing more, what is the minimum number of CBR tests required for a road project, short or long?
Dear Dr. Ullah:
I do recommend that you refer to the materials variability chapter in "Principles of Pavement Design" by Yoder. There is agood discussion there that may be of great interest to your case.
Thansk,
Dr. Bazlamit
Thanks Dr. Bazlamit.
Do you have a copy of the book and could you share it?
Thanks Kabilan
Can you tell which of the construction standards refer to this frequency of CBR testing?
Dear Shafi ullah
Please see this Presentation. This suggestion is for borrowed materials. So I suggest this specification.
http://bbmp.gov.in/documents/10180/1277071/1.Construction+of+Subgrade+Subbase++and+Base+BBMP.pdf/83453efc-aea5-4a48-9425-309b41764d7e
This is will be the best answer for your question
It is difficult to give a rigid rule on testing frequency. Considerable input from Engineer is required.When found necessary, advice is available from R & DDivision.
Dear Shafi,
I do recommend performing DCP tests to estimate CBR on site. It's reliable and cheap, so you do not have to worry about the number of tests per kilometre!
The ASTM standard is D 6951 – 03 "Standard Test Method for Use of the Dynamic Cone Penetrometer in Shallow Pavement Applications"
A lot of literature on the subject is also available on the web, especially from the Corps of Engineers. Essentials info here: http://profemery.info
Regards,
Andrea
Thanks Kabilan and Andreas for sharing valuable information on CBR and DCP.
Dear Shafi,
the number of CBR test depend on the uniformity of soil but also on technical specifications for geotechnical works which you have in your country. For the design purpose (new road) we often use one CBR test every 1000 m. If we make a reconstruction project (existing road) we often use FWD.
Regards, Tanja
Thanks a lot Tatjana.
I see that the CBR test frequency should be somewhere in between 500 m to 1000 m but I did not find this frequency in the relevant standards such as ASTM Designation D4429 or D1883. Which Codes and Standards of pavement design are you using in Croatia? And could you mention some reference document(s) for the aforementioned frequency, please?
Dear Dr. Ullah:
I will scan some relevant pages for you and send them
Dear Shafi:
Sorry for the delay. Here is the info I promised . Hope this will help
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