Soaked Cbr Value Determination from Laboratory Dcp Test for Addis Ababa Red Clay Soil
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Date
2016-06
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Addis Ababa University
Abstract
The CBR test is the most widespread method of determining the bearing strength of pavement
materials and is fundamental to pavement design. Almost all road construction manuals of
Ethiopia recommend CBR tests for flexible pavement constructions. However, most of low
volume roads such as roads built under Universal Rural Road Access Program (URRAP) have
been designed, constructed and maintained without performing the required CBR tests. One of
the cited reason is that CBR is an expensive test.
Hence, this thesis is aimed to introduce the simplest and cheapest way of determining the
required CBR values indirectly using DCP tests. In this study DCPI values obtained from the
laboratory prepared samples were correlated with soaked CBR values for Addis Ababa red clay
soils. In laboratory both CBR and DCP tests were conducted on soil samples remolded in
standard CBR molds. The tests were performed for both soaked and un-soaked conditions.
Besides, the appropriate soil index tests were conducted for all of the samples.
The data analysis was made using a statistical software called SPSS, and a good correlation was
obtained between soaked CBR and soaked DCP values and change in moisture content. Using a
multiple linear regression for 21 samples, the following empirical equation was developed with
72.9% coefficient of determination.
S_CBR = -0.53(CH_DCP_moist) - 0.22(S_DCP) + 19.49
-where; S_CBR and S_DCP are to mean that Soaked CBR and Soaked DCP respectively, and
CH_DCP_moist is the difference between the water contents of the sample before & after
soaking the remolded sample for DCP tests.
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Civil Engineering