Subgrades and pavements - Geotechnical Investigation and Design Tables - page 167

•

A minimum subgrade modulus for base course CBR modulus to apply (Hammitt,
1970).

•

CBR BC = 5.23 CBR SG .

13.27 Elastic modulus of asphalt
•

Asphalt strength varies with temperature.

•

Weighted Mean annual temperature (WMAPT) is used. These temperatures
correspond to depth of 50mm to 75mm for the asphalt layer.

•

Asphalt is a visco-elastic material but at normal operating temperatures, it may
be treated as an elastic solid.

•

Asphalt response is linear below 1000 microstrain.

•

Other variables such as air voids, asphalt content, loading rate, age of asphalt,
etc, also affect the modulus values.

•

Poisson's Ratio of 0.4 typical.

Table 13.27 Asphalt temperature zones and corresponding modulus.

Typical queensland area Temperature Representative Asphalt

range ◦ C temperature ◦ C modulus MPa

Western Queensland, Mt Isa, Cairns, WMAPT 35 36 970 >

Townsville, Barcaldine
Roma, Gladstone, Mackay, Gladstone 35 WMAPT 32 30 1400

> >

Brisbane, South East Queensland 32

>

WMAPT

>

29 30 2000

Toowoomba,Warwick, Stanthorpe 29 WMAPT 28 2500 <

13.28 Poisson ratio
•

Some variability is likely in the vertical, horizontal and cross direction for all
materials.

Table 13.28 Poisson ratio of road materials.

Material Poisson ratio

Asphaltic 0.40

Granular 0.35

Cement Treated 0.20

Subgrade soils 0.25 to 0.40

Weathered Rock Subgrade 0.3

Unweathered Bedrock Subgrade 0.15

•

Variation of Poisson Ratio values close to the above values typically has little effect
on the analysis.