Page 70 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

Table 24. Percentile Levels Recommended for Data Processing
for Flexible Pavements
Road Category Percentage of Road Allowed Recommended
to Perform Unsatisfactorily at Percentile Level for
the End of the Design Period Data Processing
A 5 95
B 10 90
C 20 80
D 50 50

The classification system used for visual condition and surveillance measurements is based on the Road Category,
and therefore the appropriate percentile value, and pre-defined criteria for each measurement type. These criteria
are set out in Appendix 1 of TRH12. Assessment criteria for rigid pavements are included in Table 2 of this chapter.
The length of pavement used to classify the pavement is generally a uniform section, for which the particular type of
measurement seems consistent. Chapter 6: 7 contains discussion on all measurement types and the associated
criteria.

The data processing, and specifically the classifications, is done with a view to collating the results to obtain a
condition assessment.

The initial estimate of the past and future traffic demand is done in accordance with the calculations set out in
Section 4.7. It is normally based on traffic data from network level observations.

(iii) Pavement Evaluation and the Initial Structural Capacity Assessment
All the information available from the initial assessment phase is used to identify uniform, or homogenous, sections
with consistent problems and rehabilitation needs over the length of the uniform section. This includes the
pavement structure information, probably from as-built data, visual condition survey data and non-destructive test
results. All this information should be displayed in a concise manner similar to the example shown in Figure 29 for a
flexible pavement. These types of plots are often called “stripmaps”.

The plot in Figure 29 contains the as-built pavement information and the pavement condition classification based on
the visual condition, FWD deflection, rut and riding quality data. The information for this particular case shows that
there is a change in both the visual condition and FWD deflection classifications at about km 11.77. At chainages
lower than km 11.77 the pavement shows very little visual distress, except for the binder condition, and all the
deflection, rut and riding quality parameters are low. The classification of the pavement condition at chainages less
than km 11.77 is mostly sound. Higher than km 11.77, the pavement shows visual distress and the deflection and
riding quality parameters are higher, resulting in warning to severe classifications for a number of parameters. The
section of road shown in the example should be divided into two uniform sections at km 11.77.

Similar stripmaps can be prepared for concrete pavements by considering the failure mechanisms of concrete
pavements as described in M3-1 or TRH19.

Once the project has been divided into uniform sections, an initial structural capacity assessment is done for each
uniform section. It is recommended that this initial structural capacity assessment is done using simple, empirically
derived relationships, such as (included in Section 7):
• Surface deflection methods
• DCP method, if DCP tests were done during the initial assessment and rut results are available
• AASHTO SN method, if riding quality results are available
• Pavement Number method

A more detailed and/or sophisticated structural capacity assessment is done during the rehabilitation design stage.

Measurement Types and Associated Criteria Visual Assessment Surveys
The most critical aspect of the visual
Chapter 6: Road Prism and Pavement Investigation,
Section 7, contains discussion on all measurement types inspection is for the team doing the visual
and the associated criteria. inspection to be properly trained and
consistent in their evaluation of distress.

Section 5: Pavement Investigation and Design Process
Page 59