Estimation of the california bearin gratio (CBR) of compacted soils using simple soil indices

The California Bearing Ratio (CBR) test is widely used to assess the stiffness modulus and strength of the base and subbase materials of earth structures such as roads dams, retaining structures, pavement and airport covers. The CBR is typically performed on compacted soil samples in the laboratory, while in the field its performed at ground surface, or on a level surface excavated in a test pit or a trench. The scope of this investigation is to develop an empirical equation relating the soil properties to CBR. Herein, Vp is a much better indicator than other soil properties in estimating the CBR values, because Vp is a function of the density and elastic modulus and is also widely used to estimate the strength of materials. Simple and multi regression analyses were carried out using experimental data to evaluate the relationship between CBR and Vp for soils. The standard error associated with the empirical relationships is very small, and the reliability and accuracy of the relationship in assessing the CBR indirectly seems to be higher than those of traditional relationships between the CBR and soil properties groups such as gradation, plasticity and compaction. The Vp values were also correlated with each soil parameter in these soil properties groups. It was found that Vp has good or strong correlations with all soil parameters affecting the CBR. These simple and multi regression models between Vp and CBR are proposed for reliable indirect estimation of the CBR in practical applications. Key words: California Bearing Ratio (CBR), Maximum Dry Unit Weight (γk), Optimum Water Content (Wopt) and Correlation Ultrasonic Pulsation Rate (Vp).