Technical information

3-9
compaction to 7.2 psi at 97.5% compaction; at a moisture level of 9.8%
6
k
was found
negligible (in the low density case).
The as-constructed subgrade moisture content at NCAT was about 10.5% (see
Chapter 2, Subsection 2.2.2) and about 14.5% in the APT (see Section 3.3). Based on
the above results the suction component in the subgrade should be negligible. The as-
constructed base moisture content was 6.5% at NCAT (see Chapter 2, Subsection 2.2.3)
and about 3.5% in the APT (see Section 3.3). Hence, the suction component in the base
can be estimated at around 7 psi (48.3 kPa); this is equivalent to a weight of 86 in. (2.2
m) of base material with a total (wet) density of 140 pcf (2245 kg/m³).
Table 3.3.1: Resilient modulus of unbound materials (calibrated equation 3.3.2
parameters).
Material Compaction, % k
1
k
2
k
3
k
6
, psi
Subgrade Soil 96.0 554 0.827 -0.770
4.8 (
%2.7=
ω
)
0.0 (
%7.9=
ω
)
0.0 (
%1.20=
ω
)
Aggregate Base
93.0 477 0.999 -1.580
2.0 (
%3.5=
ω
)
0.0 (
%8.9=
ω
)
97.5 527 0.833 -0.715
7.2 (
%5.5=
ω
)
The entire set of test data and model forecasts are cross plotted in Figure 3.3.1
(log-log scale). The goodness of fit may be graphically assessed from this figure. As can
be seen all the data points fall very close to the equality line (oblique dashed line). It
may also be seen that the resilient modulus of the subgrade at 96% compaction (square
markers) ranges between 4,500 and 15,000 psi (31 and 103 MPa). The aggregate base at
93% (triangular markers) has modulus values in the range of 4,000 to 10,000 psi (28 to
69 MPa). The resilient modulus of the 97.5% base (circular markers) has a range of
13,000 to 21,000 psi (90 to 145 MPa). It should be noted that, for the tested conditions,
considerable overlap is seen in the modulus ranges of the subgrade and base. This
means that they may exhibit comparable stiffness as part of the pavement system.