Page 118 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

7.9 Summary of Suitability of Structural Design Methods for Flexible Pavements

Table 47 provides a summary of the potential application of the structural design methods discussed in the preceding
sections.

7.9.1 Comment on Determining Remaining Life
One of the key aspects in the analysis of a pavement for rehabilitation is determining the remaining life. All of the
structural design methods discussed, except the AASHTO SN method, actually determine the structural capacity from
the initial conditions, and do not consider the observed distress, i.e., rut depth. There is no widely accepted method
used for adjusting the structural capacity estimate from the initial conditions using the current condition to obtain the
remaining life. Jordaan (1989a) provides some indications for incorporating the observed distress, or the simple
method discussed for the DCP in Section 7.3 is an approach used. The analysis method suggested by Wolff (1993,
1994) for granular materials (Section 7.1.2(ii)) is an example of an approach that directly uses the current condition
in estimating the remaining life.

Table 47. Potential Application of Structural Design Methods

Method Potential Application
New Rehabilitation Design
Design Initial Assessment Rehabilitation Design –
– Remaining Life Future Structural
Capacity

SAMDM for flexible pavements  Not practical 
Pavement Number method   
DCP design method   

AASHTO SN method   (with riding quality 
results)
FWD deflection bowl parameter method   
1
FWD SN method   
TRRL surface deflection method   

AI surface deflection method   
Notes
1. Suitable for rehabilitation design if used in conjunction with AASHTO Method.

7.10 Software Packages for Flexible Pavement Design
Software packages are available to assist with various tasks of the pavement design process, including design traffic
estimation, design investigation, pavement modelling and analysis as well as structural capacity estimation. The
purpose of these packages is to facilitate capturing, storing, processing and analysing of large volumes of data in a
fraction of the time required to do a single analysis by hand. The intention is to improve the design engineer’s
efficiency and to create a better understanding of the design problem, by including more data in the analysis and
interpretation than is possible without the software. These software packages are not intended as “black-box”
solutions, and should never be regarded as substitutes for engineering knowledge and expertise, but rather as
supplements to engineering knowledge, expertise and the design process.

This section presents a brief overview of the software packages available for flexible design. Rigid and block
pavements are dealt with in Sections 8.4 and 9.6. These packages were not critically evaluated and it is not the
intention to compare them or to endorse a specific package. Only the salient features of the software are described,
refer to the software vendors for detailed information on the functionality of the software.

7.10.1 CYRANO
Cyrano was developed by Dr Pieter Strauss and Dr Martin Slavik, and is obtained by contacting martins@bks.co.za.
Cyrano is largely based on the South African Mechanistic-Empirical Design Method (SAMDM) with the following
modifications and additions:

Section 7: Structural Capacity Estimation: Flexible Pavements
Page 107