Assessment of Falling Weight Deflectometer Data for Stabilized Flexible Pavements

Backcalculation of pavement moduli through the utilization of the falling weight deflectometer (FWD) is used for pavement monitoring and evaluation. The performance and structural condition of nine flexible pavement test sections built in Bedford County, Virginia, have been monitored over the past 5 years using FWD. The nine sections include three groups with aggregate base layer thicknesses of 100, 150, and 200 mm, respectively. Sections 1, 4, and 7 are control, whereas Sections 2, 5, 8 and 3, 6, 9 are stabilized with geotextiles and geogrids, respectively. The FWD testing used five double-load drops ranging from 26.5 to 58.9 kN. The deflection basins obtained from the testing have been analyzed using the ELMOD backcalculation program to find the pavement structural capacity and to detect changes in the aggregate resilient modulus. The analysis shows a reduction in the backcalculated resilient modulus of the 100-mmthick base layer. The reduction was 33 percent over 5 years for the nonstabilized section compared with the geosynthetically stabilized section. The reduction in base layer resilient modulus may have resulted from subgrade fine migration into this layer as confirmed by excavation. The study confirms the effectiveness of using woven geotextile as a separator in a pavement system built over weak subgrade. This supports the continuous rutting measurements and ground truth excavation conducted in late 1997.