Predicting California bearing ratio of foundation soil using ultrasonic pulse velocity

The California bearing ratio is a simple load-penetration test for determining the bearing capacity of soil being used as a foundation subgrade, subbase or base course. There are many empirical models to determine the ratio from soil index properties, but most of these are unsatisfactory. The scope of the investigation reported in this paper was to assess the reliability and accuracy of using ultrasonic pulse velocity for reliable estimates of bearing capacity. Ultrasonic pulse velocity is theoretically a much better indicator than other soil properties for evaluating bearing capacity as it is a function of density and elastic modulus and is strongly affected by material strength. A large-scale regression analysis was carried out using experimental data to evaluate the relationship between California bearing ratio and ultrasonic pulse velocity. Attenuation of ultrasonic waves was also investigated for measuring soil gradation, plasticity and compaction properties. It was found that the reliability and accuracy of ultrasonic pulse velocity in assessing the California bearing ratio indirectly seemed to be higher than those of traditional relationships between the ratio and these soil properties. These strong relationships are proposed for engineering projects requiring estimation of the California bearing ratio.