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Converting a CBR Value into a Modulus of Subgrade Reaction

Converting a CBR Value into a Modulus of Subgrade Reaction

Converting a CBR Value into a Modulus of Subgrade Reaction

(OP)
As the title states I am looking to convert the CBR value of a poorly graded sand and gravel into a modulus of subgrade reaction to be used in foundation design (not pavement design). I have found some information related to this while searching through this forum and others, however I am finding it difficult to find specific references for CBR to k for foundations.

The average CBR for the material at 95% Modified Proctor density is 30 (measured at 0.2").

RE: Converting a CBR Value into a Modulus of Subgrade Reaction

I think that CBR is used for pavement design and therefore you will find that the correlations to K-values are more related to pavements and slabs-on-grade. I saw K-values for foundations which the main parameter is the soil modulus (E).

RE: Converting a CBR Value into a Modulus of Subgrade Reaction

Agree with Okiryu....

The "k" value used for foundation design is about 1/4 of the "k" used for pavement design.

A "k" value of 50pci is actually a relatively high value, whereas a "k" value for pavement modulus of subgrade reaction would be on the order of 150 to 200, in similar soils.

RE: Converting a CBR Value into a Modulus of Subgrade Reaction

Ron, is that difference due to the size of the plate when doing plate bearing tests in order to obtain "k"? (30" vs. 12" plate sizes)

RE: Converting a CBR Value into a Modulus of Subgrade Reaction

Okiryu...actually the 12" plate will result in a higher "k" value.

RE: Converting a CBR Value into a Modulus of Subgrade Reaction

Hi Ron, agree with you. In Japan we use this correlation between k30 and k12: k12 = 2.2 x k30

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