Developing Correlations between Dynamic Cone Penetrometer and Cbr for Subgrade Soils In Addis Ababa

Abstract

California Bearing Ratio test is used to value the suitability of the sub grade and the materials used in sub base and base course. This test can be done in the laboratory as well as in the field. Dynamic cone penetrometer is an instrument used to evaluate insitu strength of pavement base, sub base and sub grade materials. But CBR testing is relatively an expensive, time consuming test and has low repeatability. Moreover, it is very difficult to mould the sample at desired insitu density in the laboratory. Therefore, to overcome these problems, the other method (Dynamic Cone Penetrometer) is used in this study. This device is cheap, portable and less time taking. A study was carried out to find the correlation between Cone Penetrometer (DCP) with CBR values that best suit subgrade soils. Accordingly, several laboratory tests and field tests in Addis Ababa has been conducted on 10 test pits with three layers. From the tests, the Atterberg limits (PI, LL, and PL), In situ density, classification (sieve analysis), California bearing ratio, insitu Moisture Content, and Dynamic cone penetration results are acquired. Based on this laboratory and field test results analyses were carried out using SPSS software. After seeing the scatter diagram it is observed that DCPI is highly influenced by natural moisture content and in situ density. It is also found out a good relationship does exist between DCP and CBR. In order to find out an expression that best suits the value of CBR from DCP and other parameters different techniques are used. The accepted one is the expression developed by using two stage residual inclusion estimation using as variable. From the analysis result gives the following equations with coefficient of determination of R 2 =0.827