Page 16 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

2. DESIGN PRINCIPLES
Typical examples of the three types of pavements; flexible, rigid and block pavements, are shown in Figure 2. This
section discusses the design principles associated with these three pavement types.

Flexible Pavement Rigid Pavement Block Pavement
Figure 2. Typical Pavements

2.1 Flexible Pavements
The basic principles of structural design of a flexible pavement are explained using Figure 3, which shows a multi-
layered pavement system loaded by a dual-wheel, half-axle load. The stresses imposed by the tyres at the tyre-
pavement interface, also called the tyre-pavement contact stress, are applied to a relatively small contact area.
These stresses are dissipated or spread over an area that increases with increasing depth in the pavement structure.
The stress concentration and shear stress, therefore, reduce with increasing depth. This is indicated by the
red/yellow shaded area. The materials in the upper region of the pavement structure therefore need high shear
strength to resist the imposed shear stress conditions. Deeper down in the pavement structure, less shear strength
is required.

Figure 3. Stress Distribution in a Typical South African Flexible Pavement

Given this stress dissipation and material strength requirement, the five principles of the structural design process for
flexible pavements are:
• Select materials of sufficient strength and stiffness for the pavement structural layers, to resist the high
imposed shear stresses and to dissipate the high imposed stresses.
• Select sufficient structural layer thickness to ensure that the subgrade material is out of the high stress
region.

Section 2: Design Principles
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