Evaluation Of Correlation’s Between Cbr Using Dcp With Laboratory Cbr At Varying Energy Levels
Subgrade soil is an important element in designing flexible and rigid pavement roads. The efficiency of pavements primarily depends on the strength and rigidity of the subgrades. The geotechnical assessment of sub grade soil materials, irrespective of being used for filling or cutting, has always been the foremost step in the construction of road pavements. In monitoring and evaluating road quality, the need for strength parameters of subgrade soils is quite significant. Indian Norm IRC-37-2012 deals with the flexible pavement design and proposes the California Bearing Ratio (CBR) as a subgrade strength predictor. The California Bearing Ratio laboratory evaluation is beneficial in the design of flexible pavements and unconfined compression strength (UCS) is useful in determining shear strength but are time-consuming parameter, and requires considerable effort besides these this conventional CBR testing has low repeatability and expensive. Furthermore, in the laboratory CBR test it is very cumbersome to remould the sample to the desired in situ density, due to stress release and dampness of surface water during sampling, in-situ values are underestimated. This paper presents the empirical correlations formed between CBR, UCS and DCPI besides these correlations CBR was also correlated with geotechnical parameters. Power regression models were found in the best fit, when connecting CBR with DCPI value and shows a strong correlation with a coefficient of determination (R2), varying between 0.96 to 0.99 for unsoaked and soaked conditions respectively and linear regression models were developed for connecting CBR with geotechnical parameters such as maximum dry density with R2 having a value of 0.73 and 0.91 and standard error of estimation of the order of 3.38 and 0.64 for unsoaked and soaked conditions respectively .The empirical correlations which have been established can be useful in determining the subgrade strength parameters quickly.