Impact of natural site variability on nondestructive test deflection basins

A series of nondestructive tests (NDT) using a falling-weight deflectometer and Dynaflect was performed at 20 test locations in Arizona. Deflection basins were obtained at 10 ft (3 m) intervals over 90 ft (27 m) length of highway. A statistical analysis of site variability, based on NDT test data, was conducted. The variability in deflection basins was found to result primarily from spatial variability of the subgrade materials. Results from cone penetrometer tests conducted at NDT test locations showed considerable spatial variability of subgrade materials both vertically and horizontally. Variation in pavement system response resulting from pavement and subgrade material stress-level-induced nonlinearities was found to be insignificant. Recommendations for assessing the significance of natural site variability are made, and a procedure for selecting analysis sections for overlay design purposes is suggested. A technique is also suggested for selecting length of test sections for NDT that takes into consideration a statistical characterization of the amount of variability at the site.