Integration of Traffic Speed Deflectometer and Ground-Penetrating Radar for Network-Level Roadway Structure Evaluation

The project has focused on the East Idaho Loop Corridor (EILC), representing 518 mi of primary roadways covering a wide range of geographic conditions. The Idaho Transportation Department (TD) has pursued this effort to support future project planning and design efforts and advance the management of its assets into a more efficient, best-first set of priorities. The EILC was surveyed with a traffic speed deflectometer (TSD) and with ground-penetrating radar (GPR). After preliminary review of the TSD data, segments were selected for falling weight deflectometer (FWD) testing to confirm patterns observed in the TSD data and to adapt FWD analysis methods to the TSD data. Ninety-nine borings were taken to confirm the pavement layer structure and verify thickness calculations. The Idaho TD data were analyzed at a 10-m interval with the GPR layer thickness data to determine subgrade modulus, pavement modulus, and structural number. These values were then used to estimate overlay requirements and, given traffic projections, to calculate the remaining life as a continuous function of roadway position. The data were incorporated into a spatial geodatabase that provides the Idaho TD with a convenient means to visualize and evaluate the overall condition of the network down to the detail of its individual segments. The segments were subdivided into homogenous sub-sections on the basis of remaining life, and these subsegments were used for identifying and programming rehabilitation projects. The level of condition detail available at the subsegment level allows for pavement design and for scoping restoration projects.