Correlation between SPT N value and CBR

[geotech888]

Hi... Fellow Engineers.

I am woring on Australian project where about 90 Kms road and rail network is required to be designed. I have the preliminay geotechnical investigation data indicating field SPT N values at various locations. I need to know the CBR value that can be adopted for the preliminay design and estimation.

Please guide If any one has got the approach to evaluate CBR from SPT N vlaues.

 

[garbageengineer]

There are tables in Chapter 5 of Burt Looks 'Handbook of Geotechnical Investigation and Design Tables' for correlating SPT and DCP blows with CBR.

 

[geotech888]

Dear garbageengineer,

Thanks for sharing the relationship, however it is not clear that the given CBR shall be considered as 4 days soak, 7 days soak or Unsoaked. The one which I required is 4 days soaked, can it be directly refer for determining subgrade thickness.