Page 66 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

Table 23. Framework for Rehabilitation Investigation and Design

Main Component Activity Elements
• Client brief
• Available information (traffic, environment)
Gathering information
• Detailed visual inspection
• Pavement surveillance measurements
• Traffic data
Data processing • Visual inspection data
Initial
assessment • Surveillance data (rut, profile, deflection)
• Condition assessment
• Demarcation of uniform sections
Pavement evaluation and • Backcalculation of deflection data (if
initial structural capacity applicable)
2
estimation
• Initial structural capacity assessment
Design • Uniform section reports
Investigation • Test-pits and bulk samples for laboratory
testing
Additional testing • Relative movements at joints and cracks
• Cores and DCP tests
Detailed • Detailed traffic survey
assessment
Cause and mechanism of • Pavement condition and behavioural state
distress • Distress manifestation and correlations
Pavement situation
description • Update uniform section reports
• Material availability and cost
Design Practical and functional • Constructability
considerations aspects • Performance adequacy
• Maintainability
Identify rehabilitation • Eliminate weak layers and utilise existing
options (design strength
alternatives) • Refer to design considerations (Section 3)
Rehabilitation Design 1
Structural pavement • Select appropriate design method(s)
design • Prepare design method inputs
• Structural capacity estimation and design
• Decide on cost elements to consider
Present worth of cost • Develop life cycle strategy for design
(PWOC) analysis alternatives
• PWOC calculation
Economic Analysis
• Decide on different strategies
Incorporation of • Assign probabilities and outcomes
uncertainty • Calculate expected PWOC for each option
• Calculate expected PWOC for each strategy
Note:
1. It is generally recommended that more than one design method is used to determine appropriate pavement structures.
2. Backcalculation is a specialist exercise and should only be done by knowledgeable engineers. See Chapter 6: 7.3.4.1 a
discussion on backcalculation.

5.1 Design Investigation
The first step for both new and rehabilitation design is the design investigation. The main purpose is to gain a
comprehensive understanding of the design problem, the parameters governing the design and to obtain the
necessary design inputs. The importance of the activities associated with the design investigation should never be
underestimated. The eventual design is only as good as the information gathered during the design investigation,
and incorrect design input from the design investigation may lead to significant design risk.

The design investigation begins with determining, in conjunction with the road authority, the design strategy. This
includes determining the appropriate road category, design structural capacity, analysis and structural design periods
and possible stage construction. The design strategy may also be influenced by the future maintenance and
rehabilitation strategy for the road. For example, certain roads may need designs that do not require frequent
maintenance, to limit traffic disruptions. Therefore, the life cycle strategy for the road needs to be determined. For
this, the initial traffic demand is required, which may be obtained from past traffic surveys on the road and road

Section 5: Pavement Investigation and Design Process
Page 55