Page 13 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

Figure 1. Effect of Traffic and Environment on Performance of Roads with Different Traffic
Levels

The functional service level largely determines how the road user
experiences the service provided by the road, and includes aspects
of safety and ride comfort. The geometric design also contributes
Routine Road Maintenance to the road-user’s perception of the level of service, but falls
Pavement design methods assume routine outside the scope of this manual.
maintenance is done on all roads. A good
reference for routine maintenance is: The structural service level reflects the condition of the pavement
system and is determined by the level of structural deterioration.
• SANRAL. 2009. Routine Road The structural condition of a pavement is generally affected by
Maintenance Manual. Second cracking, i.e., fatigue damage, and permanent deformation (or
Edition. rutting) of flexible pavements, rutting of concrete block pavements
and defects such as joint spalling and faulting, slab cracking and
punch-outs of rigid pavements. The different distress types in pavements are discussed in Chapter 14: 3. The most

common source of problems in a pavement is the ingress of moisture.

A distinction is drawn between structural distress, terminal structural condition and structural failure.
• Structural distress occurs from the day the pavement is opened to traffic. Incremental permanent deformation
and fatigue occur throughout the service life of the facility, but initially the level of distress is insignificant.
• A terminal structural condition is reached when the level of distress reaches a predefined, unacceptable level.
Examples of terminal conditions are 20 mm of rutting for flexible pavements and 5 mm of faulting for rigid
pavements. Although a terminal (unacceptable) level of distress is reached, the pavement has not necessarily
failed in the strict sense of the word. For example, the rut may be rectified with a levelling course and the
pavement may continue to provide years of excellent service.
• Structural failure occurs if the pavement layer or layers lose
strength. For example, if rutting results from unstable, rapid
shear failure, the layers do not have sufficient strength and the Functional Capacity
pavement requires structural strengthening. The functional capacity or service life is
defined as the period from an initial
The functional capacity or service life is defined as the period from sound functional condition to a
an initial sound functional condition with subsequent routine predefined terminal (unacceptable)
maintenance only, to a predefined terminal (unacceptable) functional functional condition. This is determined
condition. For flexible pavements, this is determined by functional by functional deterioration in terms of
deterioration in terms of skid resistance, loose material, potholes and skid resistance, loose material, potholes
riding quality. The functional condition may often be improved and riding quality. The functional
through maintenance alone, but the improvement of a poor riding condition may often be improved through
quality may require light rehabilitation in the form of an overlay. In maintenance alone, but the improvement
many cases, functional distresses are manifestations of structural of a poor riding quality may require light
deterioration. rehabilitation in the form of an overlay.

Section 1: Introduction
Page 2