Evaluation of Deflection Bowl Parameters in Low-Volume Roads

Evaluation of pavement deflection bowl using nondestructive testing (NDT) is an ideal method for assessing the structural capacity of individual layers of a pavement system. However, the cost of modern NDT equipment and the complexity involved in the back-calculation process makes it difficult for the road agencies to back-calculate individual layer properties and evaluate the in situ condition of existing pavements. This study developed low-cost equipment (LCE) for evaluating the pavement deflection bowl under static loading conditions and to correlate the results with the deflection bowl observed under dynamic loading on same pavement combinations. The study also analyzed the deflection bowl parameters through an understanding of the load distribution evaluated using linear elastic software. The moduli of the individual pavement layer were back-calculated using back-calculation software and correlated with the deflection bowl parameters. The study concluded that the deflection bowl under dynamic loading was only 0.65-0.75 times that of the deflection bowl under static loading. The difference of deflection measured at radial distances of 0 and 450 mm of the deflection bowl correlated well with the base-layer modulus, and the difference of deflection measured at radial distances of 300 and 600 mm correlated well with the subbase-layer modulus. Based on the deflection bowl data collected from nine test sections, it was found that emulsion-treated base layers exhibited 40%-60% higher moduli values than the conventional base layers during the monsoon season. Low-volume roads with dense surface mixes 30 mm thick exhibited significantly improved structural performance compared with that of low-volume roads with open-graded surface mixes 20 mm thick with a 6-mm seal coat.