Abstract:
At present ethiopia’s infrastructure is expanding rapidly. A large number of new urban and lightly
trafficked roads are planned or under construction. This in addition to maintenance of existing
roads results in large amount of material testing. The CBR is the most commonly used comprehensive test method for ensuring sub grade material
quality in road design application.
As a result, this study evolved to find the correlation between CBR values with soil index
properties specific to Azezo-Gorgora road sub grade soils. The study has examined the
feasibility of single linear regression analysis and multiple linear regression analysis in
correlating CBR value with soil index properties. Accordingly, thirty four disturbed samples
collected from different parts of selected route and the required laboratory tests have been
conducted in order to achieve the intended correlations.
Specific to this research, statistical software (SPSS) is employed to investigate the significance
of individual independent variables. The correlation is established in the form of an equation of
CBR as a function of grain size parameter, Atterberg limits and compaction parameters by
considering the effect of an individual soil properties and effect of a combination of soil
properties on the CBR value. The developed correlation entailed a moderate determination
Coefficient of R
2 = 0.588 using single regression analysis, while multiple regression analysis
generated relatively an improved correlation of R
2= 0.631, for a sample size of thirty four. After
validating the developed correlation with test results, it was noted that the correlation of CBR
value with soil index properties is more applicable for preliminary characterizing the
strength of sub grade soil.
