Page 72 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

Once each lane of the full project length has been divided into uniform sections, and the initial structural capacity
assessment completed, each uniform section is classified according to:
• Sections with no significant problems therefore requiring no action. Sections with no significant problems
are those sections that can economically be kept at an acceptable level of service using routine maintenance.
These sections can be often excluded from further analysis. The underlying assumption is that if the road looks
fine, it is fine. However, if the future traffic demand is high, it is advisable to check the structural capacity of
these sections as part of the detailed assessment phase.
• Sections with only surfacing problems. Ravelling, bleeding and polishing are classified as surfacing-only
distress in the absence of other forms of distress. Further tests may be required on the surfacing material to
establish appropriate rehabilitation alternatives, but these tests are not regarded as part of the rehabilitation
design phase.
• Sections with localized problems. Areas of localised distress are identified and treated separately so as not
to influence the assessment and design of the remainder of the project, and to ensure that appropriate measures
are applied to these sections to prevent recurrence of the problem. In South Africa, inadequate drainage is by far
the most common cause of localised distress. Vegetation close to the edge of the road is normally associated
with drainage problems, as are blocked drains.
• Sections requiring structural strengthening for increased structural capacity where the estimated future
traffic exceeds the remaining life. Generally, if 25 to 30% of the pavement surface needs patching, consideration
should be given to rehabilitating the pavement.

Sections that do not fit in the above categories, or for which there is uncertainty regarding the cause of distress, or
the initial structural capacity assessment indicates a low remaining structural capacity, require further analysis during
the detailed assessment phase.

The final step of the initial assessment phase is to generate a uniform section report for each uniform section. This
summarises the data collected during the initial assessment, with recommendations for:
• Additional testing required during the detailed assessment phase.
• Remedial measures for those sections not requiring structural
strengthening. Drainage
• Sections that should be considered for structural rehabilitation. In South Africa, inadequate
drainage is by far the most
These uniform section reports are updated during the detailed assessment common cause of localised
phase, when more information becomes available. distress.

5.1.2.2 Detailed Assessment
The detailed assessment deals with those sections that are identified as probably requiring structural improvement.
There are three activities typically associated with the detailed assessment phase:
• Additional testing. The purpose is to collect any additional information required, to support tentative findings
and recommendations from the initial assessment phase and to increase confidence in the causes and
mechanisms of distress. Typically, the additional tests are intrusive tests. These may include test pits and bulk
material samples for laboratory testing, as well as cores from layers that are still effectively bound. If the traffic
information available from the preliminary investigation is doubtful, a detailed traffic survey may be included
during the detailed assessment to boost confidence in the design traffic estimate. Refer to Section 4.6 for traffic
survey options.
• Determination of the cause and mechanism of distress. The establishment of the cause and mechanism of
distress for each uniform subsection is crucial for the selection of appropriate remedial actions and effective
rehabilitation design. A sound understanding of pavement behaviour is the key to identifying the origin and
hence the cause and mechanism of distress. The aspects of pavement behaviour presented in Section 3.5 are
useful for this analysis.
• Pavement situation description:
− Type and thickness of layers
− Traffic loading, both past and future
− Environment, both temperature and moisture
− Pavement performance
− Present condition, visual as well as pavement tests
− Cause and mechanism of distress

Section 5: Pavement Investigation and Design Process
Page 61