Variation of FWD modulus due to incorporation of GPR predicted laye thicknesses

Accurate pavement material identification and layer thickness determination are indispensable in a backcalculation of layer moduli from Falling Weight Deflectometer (FWD) test. Conventionally, pavement layer material and thickness are incorporated in the FWD data analysis as collected from design history or coring. However, coring at every FWD test locations is expensive and time-consuming. It is prudent for any state agency to adopt the Ground Penetrating Radar (GPR) technology to identify materials in different layer of pavement and their as-built thicknesses. This study examines the accuracy of backcalculation of layer moduli from FWD test using GPR data. In this study, FWD test is conducted on pavement section at Milepost 141 on Interstate 40 (I-40) near Albuquerque, New Mexico. The backcalculation analysis is performed using the layer thicknesses as collected from the design history. Later, GPR is used to predict the as-built layer thicknesses of this section. Pavement layer moduli are again backcalculated using the GPR predicted thicknesses. It is observed that incorporation of as-built thicknesses in backcalculation process leads to a significant difference in predicted layer moduli. Therefore, a recommendation is made to conduct simultaneous operation of GPR and FWD test for pavement analysis and design.