Page 65 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

5. PAVEMENT INVESTIGATION AND DESIGN PROCESS
The design investigation processes are different for new and rehabilitation design. Design investigation for new
design focuses on the characterisation of the in situ subgrade and materials available from nearby sources, such as
borrow-pits and quarries. Except for the utilisation of the in situ subgrade, the pavement is constructed from new.
The design investigation for rehabilitation design aims to identify and remedy distressed and weak layers in the
existing pavement structure, and attempts to maximise use of the existing pavement structure in the design of the
new pavement structure.

For new pavements, the investigation delineates the subgrade into sections of similar quality. The rehabilitation
investigation process divides the existing project road into a number of homogeneous or uniform sections, some of
which only require remedial measures while others require structural strengthening to accommodate the anticipated
future traffic. A structural pavement design needs to be done for those sections requiring structural strengthening
similar to the structural design required for new pavements, to ensure adequate structural capacity to carry the
traffic. When the structural design is actually being done, the differences between new and rehabilitation design are
less significant. However, certain structural design techniques are better suited to rehabilitation design, while others
are better suited to new design.

Pavement design for new and rehabilitation projects are based on the same principles, design considerations and
techniques. However, the detail of the tasks performed during new and rehabilitation design is sufficiently different,
especially during the design investigation phase, to warrant separate discussion. Figure 28 presents a diagram for
new pavement design, and Table 23 provides a framework for rehabilitation design.

Client Brief:
• Service objective
• Analysis period and structural design period
• Life-cycle strategy
• Road category

Design Investigation:
• Develop a design strategy
• Traffic investigation and design traffic estimate
• Material availability, quality and cost
• Environmental considerations
• Practical considerations

Subgrade Delineation

Structural Design

Economic Analysis

Figure 28. Flowchart for New Pavement Design

Section 5: Pavement Investigation and Design Process
Page 54