Estimation of subgrade CBR

The CBR of the subgrade material can be estimated from tables derived after extensive laboratory work. Determining the design subgrade bearing capacity in terms of CBR constitutes a tedious and costly but necessary work. To reduce both effort and cost, some organisations have carried out extensive research from which tables and equations have been developed to estimate or predict the CBR values of various subgrade soil materials. 

Poor Average Good Poor Average Good  

Source Powell W.D. et al.. The Structural Design of Bituminous Roods. TRRL Laboratory Report LRI 132. Crowthorne, UK Transport Research Laboratory, 1984. 

Note PI, plasticity index Thn, thin pavementThk, thick pavement. 

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