Developing Correlation Between DCP And CBR For Locally Used Subgrade Materials
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Date
2012-06
Authors
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Journal ISSN
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Publisher
Addis Ababa University
Abstract
California Bearing Ratio (CBR) is a commonly used indirect method to assess the sub grade
soil strength in pavement design works. However, since CBR cannot be easily determined in
the field, civil engineers always encounter difficulties in obtaining representative CBR
values for design of pavement. Consequently, prediction of CBR va1ues from other direct
soil field tests such as Dynamic Cone Penetrometer (DCP) is found to be a valuable
alternative.
The dynamic cone Penetrometer (DCP) is the most versatile rapid, in situ evaluation device
currently available. Its correlations to CBR and its use in performance evaluation of
pavement layers make it an attractive alternative to more expensive and time consuming
procedures. Many useful correlations had been proposed by various researchers for soils of
their locality in which the DCP penetration index was used to develop these correlations.
A study was carried out to find the correlation between Cone Penetrometer (DCP) with CBR
values that best suit the type of soils in Ethiopia. Accordingly, several laboratory tests and
field tests on Jimma – Mizan, Contract 1: Jimma – Bonga road project from km 100+000 to
km 105+000 has been conducted. From the tests, the Atterberg limits (PI, LL, PL), In situ
density, classification (sieve analysis, hydrometer 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 and the
applicability of the existing correlations for Ethiopia soil on the aforesaid data was checked.
From the analysis results, it is observed that the published correlations are not suitable to be
used in Ethiopia. Consequently, a correlation had been proposed in the study to predict the
CBR values of the sub grade soil from dynamic cone penetration test results.
The relation obtained from statistical analysis relationship has an R
2
of 0.943 and is shown
below.
log (CBR) = 2.954 – 1.496log (DCPI) with R
2
= 0.943
The results of the statistical analysis show that good correlation does exist between the
dynamic cone penetration indexes (DCPI) and unsoaked CBR values.
Description
Keywords
DCP, CBR, Sub grade Materials