Correlation of Cbr Value With Soil Index Properties for Addis Ababa Subgrade Soils
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Date
2013-12
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Addis Ababa University
Abstract
The unique nature of soil properties as it appears naturally is that being divergent spatially and seasonally beyond the designer’s control. Geotechnical engineers usually attempts to develop empirical equations specific to a certain region and soil type. However, these empirical equations are more reliable for the type of soil where the correlation is origin. Hence, it is important to develop empirical equations that best fit for the local area that we can access.
As a result, this study evolved to find the correlation between CBR values with soil index properties specific to Addis Ababa subgrade 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, forty two disturbed samples collected from different parts of Addis Ababa 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 R2 = 0.458 using single regression analysis, while multiple regression analysis generated relatively an improved correlation of R2 = 0.629, for a sample size of forty two. After validating the developed correlation with control test results, it was noted that the correlation of CBR value with soil index properties is more applicable for preliminary characterizing the strength of subgrade soils.
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Geotechnical Engineering