Prediction of CBR Value from Index Properties of Cohesive Soils.

Abstract

The aim of this paper is to develop empirical relationship between CBR values and soil index properties
of cohesive soils as road subgrade. However; it is always difficult for highway engineers to obtain representative
CBR values for design of pavement. Over the years, many correlations had been proposed by various researchers
in which the soil index properties were used to develop these correlations. The CBR value is affected by the initial
state parameters of soil as described by the water content and dry density and the testing conditions. Silty clay soil
samples were compacted at different water contents and dry densities to measure the strength by CBR tests in
soaking and unsoaking conditions. The results show that the CBR values of these soils are greatly influenced by
the water content and dry density (i.e. the initial state parameters) of the soil as well as the testing conditions.
Analysis of the experimental data indicated that it is possible to combine these initial state parameters in a way
reflecting the influence of each of them on the CBR. Therefore a new concept has been developed; this is called
the initial state factor. This factor is also developed for the soaking or saturated condition and is called the soaking
state factor. On basis of this concept, a reliable strong correlation has been established between CBR values and
soil state factors and plasticity index. Comparison between the measured soaked or unsoaked CBR values and the
calculated results using the developed equations clearly indicates the reliability of these equations