Using geosynthetics in flexible airport pavements 12" Diameter Plate 6.0" 18.125" 29.125" 29.125" 18.125" 6.0" 5.0" Hot Mix Asphalt Phase I Placement 7.0" P-209 Aggregate Base Course 1 in. Phase II Placement 12.0" P-154 Aggregate Subbase 1 in. 6 ft. LVDT Earth Pressure Cell 2 in. 28" CH Subgrade (CBR = 3) 6 ft. Instrumentation Profile View FIGURE 4 Instrumentation plan FIGURE 5 Five-inch (127 mm) P-401 surface deformation 30 Geosynthetics | June July 2019 Pore Pressure Transducer (not to scale) placed at the base course/subbase interface can significantly improve rutting performance. This is reiterated by the calculated TBR values ranging from 3.3 to 29.7 at the 1-inch (2.5-cm) and 2-inch (5.1-cm) failure criteria. The lower TBR values reported for Test Item 2 may be attributed to the reduced P-209 base course thickness of 1 inch (2.5 cm), as shown in Table 4 on page 27. However, literature has shown that geosynthetics may provide a reduced layer thickness benefit, while maintaining improved structural performance. The Phase II results shown in Figure 5 show less consistent performance benefit when placed deeper in the pavement structure at the subbase/subgrade interface. The Phase II TBR values, ranging from 0.4 to 2.6, show a reduced performance benefit when compared to the results of Phase I. This suggests that geosynthetics placed deeper in the pavement structure reduce the realized benefit. It was identified that TBR values of Test Item 7 and 10 exhibited an increase in TBR at the 2-inch (5.1cm) compared to the 1-inch (2.5-cm) deformation criteria. This suggests that increased loading and deformation may be required to engage the geosynthetic product and achieve a realized benefit when placed deeper in the pavement structure. Therefore, placement of geosynthetic product closer to the structural surface loading may be desirable to achieve the maximum benefits prior to significant deformation. The total cycles applied and the postloading pavement layer deformations data are shown in Table 7 on page 29. The Phase I results show the geosynthetic-reinforced test items provided an overall structural benefit by reducing individual layer deformation at increased loading cycles. However, the Phase II individual layer deformation data was less consistent, showing a lesser benefit.