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surface at the center was under tension from the beginning up to 120 cycles and then became
under compression up to the end of the test even though the magnitude of the strain was small.
However, the tensile strain developed at the bottom of the HMA surface at the distance of 12.5
cm away from the center.
Strain (%)
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0
-0.001
Center 12.5 cm
0 50 100 150 200
Number of loading cycle
Figure 4.14 The strain at the bottom of the HMA surface versus the number of loading cycle for
the 15 cm thick unreinforced RAP base section
Figure 4.15 shows the measured vertical stresses at the interface between subgrade and
base at five locations (center, 12.5, 25, 50, and 75 cm away from the center) versus the number
of loading cycles. It is shown that the vertical stresses at the center or close to the center were
much higher than those away from the center. The vertical stress at the distance of 75 cm away
from the center was almost zero. As discussed earlier, the vertical stress at the center was used to
calculate the stress distribution angle. The stress distribution angle versus the number of loading
cycles is shown in figure 4.16. The stress distribution angle decreased with an increase of the
load cycle and remained almost the same after 50 loading cycles.
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