Developing Correlation Between Dcp And Cbr For Locally Used Subgrade Materials

California Bearing Ratio (CBR) is a commonly used indirect method to assess the sub gradernsoil strength in pavement design works. However, since CBR cannot be easily determined inrnthe field, civil engineers always encounter difficulties in obtaining representative CBRrnvalues for design of pavement. Consequently, prediction of CBR va1ues from other directrnsoil field tests such as Dynamic Cone Penetrometer (DCP) is found to be a valuablernalternative. rnrnThe dynamic cone Penetrometer (DCP) is the most versatile rapid, in situ evaluation devicerncurrently available. Its correlations to CBR and its use in performance evaluation ofrnpavement layers make it an attractive alternative to more expensive and time consumingrnprocedures. Many useful correlations had been proposed by various researchers for soils ofrntheir locality in which the DCP penetration index was used to develop these correlations. rn rnA study was carried out to find the correlation between Cone Penetrometer (DCP) with CBRrnvalues that best suit the type of soils in Ethiopia. Accordingly, several laboratory tests andrnfield tests on Jimma – Mizan, Contract 1: Jimma – Bonga road project from km 100+000 tornkm 105+000 has been conducted. From the tests, the Atterberg limits (PI, LL, PL), In siturndensity, classification (sieve analysis, hydrometer analysis), California bearing ratio, insiturnMoisture Content, and Dynamic cone penetration results are acquired. Based on thisrnlaboratory and field test results analyses were carried out using SPSS software and the rnapplicability of the existing correlations for Ethiopia soil on the aforesaid data was checked.rnFrom the analysis results, it is observed that the published correlations are not suitable to bernused in Ethiopia. Consequently, a correlation had been proposed in the study to predict thernCBR values of the sub grade soil from dynamic cone penetration test results. rnrnThe relation obtained from statistical analysis relationship has an Rrn2 rnof 0.943 and is shownrnbelow. rn rn log (CBR) = 2.954 – 1.496log (DCPI) with Rrn2rn = 0.943rnrnThe results of the statistical analysis show that good correlation does exist between therndynamic cone penetration indexes (DCPI) and unsoaked CBR values.

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