Subgrades and pavements - Geotechnical Investigation and Design Tables - page 163

•

Pavements for unsealed roads/rural roads/light traffic based on 80% probability
level.

•

Pavements for sealed roads/moderate to high traffic based on 90% probability
level - slighter thicker pavement.

13.20 Typical CBR values of pavement materials
•

The modified compaction is typically applied to paving materials.

•

The achieved density and resulting CBR is higher than the standard compaction
result.

•

The modified CBR result for the full range of USC materials is provided for
completeness, but non granular materials would not be applicable to paving
materials.

Table 13.20 Typical CBR values for paving materials.

Soil type Description USC symbol CBR % (Modified)

Gravels Well graded GW 40-80

Poorly graded GP 30-60

Silty GM 20-50

Clayey GC 20-40

Sands Well graded SW 20-40

Poorly graded SP 10-40

Silty SM 10-30

Clayey SC 5-20

Inorganic silts Low plasticity ML 10-15

High plasticity MH 10 <

Inorganic clays Low plasticity CL 10-15

High plasticity CH 10

<

Organic With silt/clays of low plasticity OL 5

<

With silt/clays of high plasticity OH

<

5

Peat Highly organic silts Pt 5 <

•

Actual CBRs depends on the grading, maximum size and percentage fines.

13.21 Typical values of pavement modulus
•

Pavements require compaction to achieve its required strength and deformation
properties. The level of compaction produces different modulus.

•

Existing pavements would have reduced values for asphalt and cemented
materials.

•

Degree of anisotropy = Ratio of vertical to horizontal modulus.

•

Degree of anisotropy = 1 for asphalt and cemented material.

•

Degree of anisotropy = 2 for unbound granular material.

•

Flexural modulus applies to pavement layers, while compressive modulus applies
to subgrade in pavement design.