Subgrades and pavements - Geotechnical Investigation and Design Tables - page 156

Figure 13.1 Seasonal and initial movements.

13.6 Subgrade moisture content
•

The key to minimising initial volume change is to place the material as close as
possible to its equilibrium moisture content and density.

•

Equilibrium moisture content depends on its climatic environment as well the
material properties itself.

•

The data below was established for equilibrium conditions in Queensland,
Australia.

Table 13.6 Equilibrium moisture conditions based on annual rainfall (Look, 2005).

Median annual Equilibrium moisture content

rainfall (mm)

WPI 1200 WPI 1200-3200 WPI 3200 < = >

(Low correlation) (Medium correlation) (High correlation)

Median value 80% OMC 100% OMC 115% OMC

for all rainfall
≤ 500 50% ∗ to 90% OMC 70% to 100% OMC 50% to 80% OMC

500-1000 70% to 120% OMC

1000-1500 70% to 110% OMC 100% to 130% OMC 110% to 140% OMC

≥

1500 130% to 160% ∗ OMC

∗

Beyond practical construction limits

•

The above equilibrium conditions also influence the strength of the subgrade.

•

Use above EMC to obtain corresponding CBR value.