CBR vs Stiffness

[CCTsurvey]

have been told that you can get the CBR (shearing strength) of a soil from its stiffness. specifically, stiffness, K = 10340 CBR. This would make my task of measuring base / subbase soil strength for aircraft cycles much easier. Is this a correct statement?

 

[BigH]

There are correlations around - Fang (Foundation Engineering Handbook) has correlations of CBR to N values etc. Baker's Highway Engineering Handbook has correlations of CBR to k values and "R" values. In the later, for instance - CBR=10, k=200psi/i; R=43; CBR=20, k=250psi/i;R=56. But, remember, these are just correlations and should be used with caution. Also, you need to understand the units - your 10340 seems like it might be SI. Also, I am not sure if the CBR quoted is the soaked or unsoaked and you need to be careful in this too.

 

[Focht3]

Hmmm,

How are you measuring stiffness?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[CCTsurvey]

Thanks Focht3,

How am I measuring stiffness - I am not. Previously the only measurement we have been concerned with is CBR. The correlation between stiffness (Young’s modulus) and ground shearing strength (to 1 m depth) is a major departure from our modus operandi and I am very skeptical. The proposal submitted intends to utilize a combination of bender element, falling weight deflectometer and continuous surface wave devices to arrive at a weight bearing result – what is your take? Could it be that simple?

 

[Focht3]

Nope.

The proposer is making a lot of assumptions to arrive at a "bearing value." Why are they proposing a non-standard approach? I assume there must be some difficulty with the site -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[VAD]

Hello CCT Survey(Military):

The value you have shown is the metric equivalent to E psi= 1500 CBR. (1500x6.89) (1psi approx 7 kPa). Refer to Yoder and Witczak 2nd Edition page 276. For other info on this correlation developed by Heukelom and Klomp, refer to "AASHTO Guide for Design of Pavement Structures" page (I-14). Hope this helps or you may have seen same already. Note that while the values for correlation vary widely, the reported correlation has been popular for soils with CBR of 10 or less.

Regards