Developing Correlation between Index Properties and California Bearing Ratio, CBR of soils: A Case Study on Gedo Menabegna Road Upgrading Project; on the Way from Gedo to Fincha

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Addis Ababa University


California Bearing Ratio (CBR) is a very common test to determine the thickness of overlying pavement layers in pavement design and to assess potential strength of subgrade, sub base and base course material. Engneers are continually searching for simplified tests with the view to increase their knowledge of soils via using a simple and rapid soil tests. These simplified tests which are indicative of the engineering properties of soils are called index properties. In road construction, civil engineers constantly come upon difficulties in obtaining representative CBR value for pavement design. Laboratory CBR test requires relatively large effort to conduct the test and it is time consuming. The alternate method could be to correlate CBR with simpler test results such as soil index properties. These tests are much economical and rapid than CBR test. This project gives an overview to obtain a correlation between CBR values with soil index properties for Gedo-Manabegna road upgrading project. Primarily, in order to address the intended objectives of the study, basic theories and descriptions of CBR test in general and in relation to index property of subgrade soil is reviewed. Subsequently, previous works of different researchers with regard to prediction of CBR value from basic soil index properties were assessed. In order to have satisfactory data for utilizing the correlations, conducted laboratory tests are collected from Gedo-Manabegna road upgrading project to get records of test results of CBR values along with the associated soil indices particularly the grain size analysis, Atterberg limits, moisture-density relationships. Then, discussions on sample collection and summary of laboratory test results are presented. Statistical regression analyses of test results carried out, correlations are developed and analyzed to fit the test results with a reliable accuracy with a higher regression coefficient that approaches to unity. Finally, a generalized conclusion and recommendation is made.



California Bearing Ratio, CBR, Index Properties, Gedo Menabegna Road Upgrading Project