Page 119 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

• The factor of safety model for unbound granular base layers (Maree, 1978; Section 7.1.2) is replaced with
the permanent deformation model developed by Wolff (1993) (Section 7.1.2(ii)).
• The principle that deformation is dependent on stress ratio is applied to calculate the deformation of the
subbase.
• Crushing of the surface of the base and the associated loss of bond between the surface and the top of the
base is based on equations developed from finite element analysis.
• The change in stiffness of the surface, base and subbase with increased load cycles or time is done through a
recursive simulation scheme.
• The outcome of the analysis, namely the percentage of the area with unacceptable cracking and
deformation, is translated into area that has to be repaired and the calculation of present worth of pavement
life cost.
• The increase in road roughness with an increase in load cycles is based on work done at the AASHTO
road test and by Ullidtz (1998).

Table 48. Functionality of the CYRANO Software Package
Application Area Aspect/Functionality Comment
Design traffic estimation Traffic data options Weigh-in motion (WIM) axle load spectra are
used. Typical default spectra are included if data
are not available.
Pavement load sensitivity From calculated pavement response under load
spectra and empirical performance prediction.
Design traffic estimation Calculated from the traffic input data.
Design investigation Input data Pavement layer characteristics and costs, traffic
loading data and environmental condition
Data analysis options Sensitivity analysis using the “What if” function
Data import, export and Summary report containing input and output
reporting
Pavement analysis and Analysis engine ELSYM 5
modelling Analysis options Analyze the effect of variation in input data on the
outcome by using the “What if” facility.
Material data and damage User defined material properties and calibration
models coefficients
Structural capacity estimation Progressive distress through a recursive
simulation scheme
Simulation schemes Monte Carlo variability Used to arrive at the predicted percentage area
simulation failed with loading or time
Recursive damage model Available as part of Monte Carlo simulation
procedure
Riding quality deterioration Based on AASHTO and calibrated for SA
conditions

7.10.2 PADS Software Series
The Pavement Analysis and Design Software (PADS) series is developed and distributed by CSIR Built Environment.
It is available directly from CSIR, www.csir.co.za. The software consists of a number of independent components
that are integrated into a single package for project level design investigation and analysis. The series consists of
the following packages:
• Traf-PADS : design traffic estimation
®
®
• Back-PADS : deflection bowl analysis and backcalculation
®
• Me-PADS : mechanistic-empirical structural capacity estimation
®
• Pro-PADS : project level design investigation and analysis

Table 49 summarises the functionality of the PADS series.

Section 7: Structural Capacity Estimation: Flexible Pavements
Page 108