Prediction of california bearing ratio (cbr) value from index propertiesofsoil for case of azezo-gorgora road

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.