Technical information

3-26
Figure 3.5.2 presents the vertical stresses measured on top of the subgrade and
on top of the base course by the four pressure gauges. As can be seen, the resulting
curves are bell-shaped and nearly symmetric. For loading pass #5,000, peak vertical
stresses on top of the base course were 30 and 35 psi (0.21 and 0.24 MPa). On top of the
subgrade, the measured peak stresses were 16 and 20 psi (0.11 and 0.14 MPa). In theory
the readings of each gauge pair should be identical. Furthermore, it may be seen that
peak vertical stresses during pass #80,000 are slightly higher compared to pass #5,000.
The difference is more significant in both absolute and relative terms for the gauges
located on top of the subgrade compared to those located on top of the base course. It
should be noted that the stress peaks occur slightly after the APT carriage had passed
over the gauges and moved further along by about 2 to 5 in. (51 to 127 mm).
0
4
8
12
16
20
24
28
32
36
40
0 40 80 120 160 200 240
APT Carriage Location [in.]
Vertical Stress [psi]
Pass #5,000
Pass #80,000
#1178,
top of base
#1179, top of
subgrade
#1184, top of
subgrade
#1185,
top of base
Loading Direction
Figure 3.5.2: Measured vertical stresses in Section n1 on top of the base and on top of
the subgrade during pass #5,000 (solid line) and pass #80,000 (dashed line).
Figure 3.5.3 presents the measured horizontal strains at the bottom of the HMA
course in the direction of loading. Four gauge readings are shown, two of which were
located along the loading centerline (G-2 and G-4), and two were located along a
parallel line (G-5 and G-7) that is offset by two feet (0.61 m); see Figure 3.5.1 and
Table 3.5.1. In all four cases it can be seen that as the load approaches a gauge, the