Page 69 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

furniture such as guardrails, signposts and fencing.
The detailed visual inspection is done to record and
map:
− Position of distress Network vs Project Level Data
− Mode and type of distress Collection and Analysis
− Degree and extent of distress Data collection and analysis at the network level is
− Spacing of distress intended to monitor the general performance of a
− Pertinent construction details and deficiencies network, and to highlight and prioritise sections for
− Topographical, geological and vegetation maintenance or rehabilitation.
clues to the cause of distress
− Condition of drainage structures and facilities Project level data collection and analysis is
• Pavement surveillance measurements. The typically a lot more detailed than network level
automation of pavement surveillance for network level analysis. It is intended to gather sufficient
pavement management has led to the increased information with which to assess the condition of
availability of valuable data, such as rut, riding quality the pavement, and to decide on appropriate
and deflections, for project level preliminary maintenance and rehabilitation measurements.
investigations. In many situations, the Road Agency’s
PMS has sufficient data for the initial assessment For example, for network level monitoring, SANRAL
phase. See Chapter 6: 7 and Chapter 14: 3.4 2 for measures FWD deflections at 200 metre intervals.
discussion on the surveillance equipment. For project level investigations, FWDs at least every
100 metres are recommended.
TMH9 provides guidance on the rating of visual distress
for flexible, rigid and gravel pavements. Although TMH9 is primarily intended for network level evaluations, it
contains useful photographic examples of flexible pavement distress. The degree rating system in TMH9 is valid for
both network and project levels. The most critical aspect of the visual inspection is for the team doing the visual
inspection to be properly trained and consistent in their evaluation of distress.

The most comprehensive method of recording distress is for inspection teams to walk the length of road (if safety
conditions allow) and to map the chainage/longitudinal distance and transverse position of the distress. This process
is, however, time consuming. If a competent team is doing the inspection, the visual distress is recorded in terms of
a degree and extent rating similar to the process used for network level evaluations. However, for project level
surveys, the segment lengths are normally reduced to 200 metres or less. The level of detail of the survey is also
influenced by the perceived remedial or rehabilitation action required. For example, if pre-treatment such as
patching followed by a surfacing is likely, then the comprehensive approach offers many benefits. If it is clear that
some form of reworking is required, then the degree and extent rating system approach may suffice.

Additional information to allow for the selection of uniform sections is obtained from non-destructive testing, such as
riding quality, rut depth and skid resistance measurements. These are used as measures of functional serviceability
of the road. Deflection measurements, Dynamic Cone Penetrometer (DCP), rut depth measurements and trial pit
results are used as indicators of the structural condition of the pavement. These are discussed in more detail in
Chapter 6: 7. The length of uniform sections varies and the delineation of these sections is often based on a
cumulative difference approach. Refer to Appendix J of the 1993 AASHTO Design Guide for details on the cumulative
difference procedure (AASHTO, 1993). Chapter 6: 7.3.4.1 contains a brief discussion of the cumulative difference
approach.

(ii) Data Processing and Condition Assessment
Data processing of the visual inspection ratings, non-destructive Visual Assessment References
test results and preliminary traffic data is done during the initial
assessment phase. The effective evaluation of the collected Visual assessments have been covered in
data requires data to be categorized against set criteria and many guidelines: M3-1, THM6, TMH12, TRH6
presented in a form that facilitates analytical comparison. and TRH19.
Therefore, performance criteria are necessary for each type of
measurement. A classification of the existing pavement A new guideline is currently being compiled,
condition and expected future behaviour as “sound”, “warning” and will be released as a revised THM6. This
or “severe” is done based on each measurement type. The TMH6 will cover all pavements types, including
classification is in terms of current condition for the visual flexible, rigid and gravel roads, and will
condition inspection data, and in terms of the current and supersede the guidelines listed above. When
expected future condition for measured pavement response. the guideline is ready it will be available on the
SANRAL website. www.nra.co.za

Different performance criteria are applied to different road
categories. Table 24 provides criteria for the percentile levels according to which the condition of the road should be
classified for flexible pavements.

Section 5: Pavement Investigation and Design Process
Page 58