Subgrades and pavements - Geotechnical Investigation and Design Tables - page 153

Subgrades and pavements

13.1 Types of subgrades
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The subgrade is the natural material immediately below the pavement.

•

The depth of subgrade varies depending on the type of load applications and the
pavement type.

Table 13.1 Depth of subgrades.

Application Type of load Pavement type Subgrade depth

Airport Dynamic/extra heavy Flexible 2.0 m

Rigid 1.5 m

Mine haul access Dynamic/very heavy Flexible 1.5 m

Rail Dynamic/very heavy Flexible/rigid 1.25 m

Major roads Dynamic/heavy Flexible 1.0 m

Rigid 0.75 m

Industrial building Dynamic/static/heavy Rigid 0.75 m

Minor roads Dynamic/medium Flexible 0.75 m

Rigid 0.5 m

Commercial and Static/medium Rigid 0.5 m

Residential buildings
Walkways/bike paths Static/light Rigid/flexible 0.25 m

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Contact pressures for flexible foundations on sands and clays approximately
similar

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Contact pressures for rigid foundations:
- On sands, maximum pressure is at middle.
- On clays, maximum pressure is at edge.

•

Test location layout should reflect the above considerations.

•

Subgrade refers to only direct bearing pressures, while material below the sub-
grade should also provide adequate support, although at reduced pressures. This
underlying material can also affect movement considerations.

•

Arguably for thick pavement designs/capping layers, the subgrade is now reduced
to the top 0.5m depth.