The deflections normally increase considerable during an HVS test, as a result of damage to the bound layers (asphalt and self-cementing AB in this case). This means that the stresses and strains in the pavement layers, which are used in calculation of the pavement performance, also change during the test. To ensure that the pavement response calculated by CalME was reasonably correct for the duration of the test, the surface deflections and the deflections at the depths of the MDD modules were calculated by CalME and compared to the RSD and MDD measurements.

Figure 1: Measured (RSD) and calculated (Calc) surface deflection versus load applications.

Figure 1 Measured (RSD) and calculated (Calc) surface deflection versus load applications. Figure 1 shows a comparison of surface deflection under a 60 kN wheel load, for the test section with a 45 mm MB15 overlay. Even though the test section is only 6 m long the measured surface deflections vary considerably over the area of the test section, sometimes by as much as a factor of 2. The coefficient of variation on the RSD measurements varies from less than 10% to more than 20%. It may be noticed that the deflection increases by more than 50% within the first one million load applications. The drop in deflection after one million load applications is due to the temperature being reduced from 20 ºC to 15 ºC. The deflections calculated by CalME are seen to be in reasonably good agreement with the average of the RSD deflections.

The three MDDs shown in Figure 2 measured the deflection at (approximately) the top of the aggregate base. They also indicate a considerable variation within the test section, and show the same trend as the RSD deflections. The deflections calculated by CalME are seen to be in good agreement with the measured deflections.

Figure 2: Measured (M, by MDD) and calculated (C) deflections, approximately on top of base