Page 94 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

Figure 34. Change from Lightly Cemented Layer to Equivalent Granular State

When the cemented layer has reached the equivalent granular state, it is analysed in a second phase using the
granular materials transfer function, with the materials properties for the equivalent granular state shown in
Table 30. The combined life of the layer is calculated from the life of both phases, as discussed in Section 7.1.7.2.
Theyse et al (1996) provides complete details.

Cemented layers are also analysed for crushing at the top of the layer, using the vertical compressive stress as
shown in Figure 35. This is particularly relevant for base layers. Crushing is not considered a terminal condition, and
hence it is not used in the critical layer calculation. However, it is an important check, as any crushing has a
significant impact on the surfacing.

Inverted Pavements
An inverted pavement is when the base layer is a
high quality granular layer, and the subbase a
cement stabilized layer. A thin asphalt layer or
seal provides the surfacing. The term “inverted”
is used because the strength of the pavement
does not decrease with pavement depth, because
of the stiff cemented layer. This means that the
pavement is not in balance. σ v

The idea behind an inverted pavement is that the
cemented layer provides an anvil upon which the ε
granular base can be well compacted. This t
achieves a high quality, dense base.

Over time, the cemented layer weakens to an
equivalent granular state. The pavement is then
in balance.

Inverted or “upside-down” pavement structures
are commonly used in South Africa, and are
included in the TRH4 catalogues. Figure 35. Critical Parameters and Locations
for Lightly Cemented Layers

Section 7: Structural Capacity Estimation: Flexible Pavements
Page 83