Page 14 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

Structural capacity or service life is defined as the period from an
initial sound structural condition to a predefined terminal condition.
The structural condition is determined by structural deterioration in Structural Capacity
terms of deformation, cracks, faulting and a loss of load bearing
capacity. Structural failure can often only be corrected through The structural capacity or service life is
heavy rehabilitation, requiring the structural strengthening or defined as the period from an initial
rebuilding of the “failed” pavement structure. sound structural condition to a
predefined terminal (unacceptable)
The structural and functional capacities are measured in terms of the structural condition. During this period
number of load repetitions to reach the terminal condition, or the only routine maintenance is performed,
time period required to reach the terminal condition. These and at the end of this period heavy
structural and function capacities are affected by the timing of rehabilitation or reconstruction is
maintenance and rehabilitation. This is discussed further in Section normally required.
3.3.

There are a number of factors that impact on the functional and structural performance, capacity and service life of a
pavement. These are the construction quality, maintenance schedule and pavement design. Together, these three
aspects determine the performance potential of the pavement. The actual performance is determined by the
environment in which the pavement operates. A pavement with a given design, construction quality and
maintenance schedule performs differently in different environments.

The balance between the potential capacity of the pavement and the demand on the pavement eventually
determines the performance and service life of the pavement. If there is an oversupply of capacity for the given
environment, the pavement will perform exceptionally well and has a service life that exceeds the originally intended
design life. Although this is a safe design approach, it has high initial costs and is probably not economically
warranted in the long-term. Similarly, if the capacity is insufficient for the given environment, the pavement
performs poorly, is unlikely to reach the intended design life, and requires regular maintenance at high costs, making
such an approach unsustainable.

Structural pavement design matches the structural capacity of a pavement with the traffic demand for the given
environment. It is inherently assumed that the design assumptions are met during construction and a proper
maintenance schedule is followed. Structural design therefore requires two components:
• A method to calculate and express the traffic demand in numerical terms.
• A method to estimate the structural capacity of a potential pavement design.

These two components of the structural
pavement design process are presented in this
chapter. The intention of this chapter is to
provide an overview of sound engineering Guidelines for Pavement Design
practice and procedures, as well as the A number of national and industry guideline documents are
techniques used during pavement design. useful for the design of new and rehabilitated pavements.
Reference should be made to the guideline These are:
documents for additional details. • Flexible pavements
− TRH4 for new design
Table 1 provides a summary of the main − TRH12 for rehabilitation design
elements of new and rehabilitation design. − TRH14 for material classification
The sections in this chapter where the topics

are covered are also given. • Rigid pavements
− M10 Manual
− Extensive documentation in the help file of cncPave.
The M10 Manual was superseded by cncPave.
Structural Pavement Design • Block pavements
Structural pavement design matches the − UTG2
structural capacity of a pavement with − Concrete Block Paving Book 2 – Design Aspects (CMA)
the traffic demand for the given • Traffic estimation
environment. It is inherently assumed − TRH16 for flexible, concrete block and rigid pavements
that the design assumptions are met
during construction and a proper These documents set out sound engineering design principles
maintenance schedule is followed. See and procedures to follow during the design phase,
Section 3.2 and 3.3 for further supplemented by the other guidelines mentioned in this chapter
discussion. and listed in the references.

Section 1: Introduction
Page 3