The growing interest in pavement management systems (PMSs), both in South
Mrica and internationally, has been in response to a shift in importance from
the construction of new roads to the maintenance of the existing paved network
coupled with increasingly restrictive road funding. In order to develop a
balanced expenditure programme for the national roads of South Africa there is
a need to predict the rate of deterioration of a pavement and the nature of the
changes in its condition so that the timing, type and cost of maintenance needs
could be estimated. Internationally these expected changes in pavement
condition are predicted by pavement deterioration models, which normally are
algorithms developed mathematically or from a study of pavement deterioration.
Since no usable pavement deterioration models existed locally, it was necessary
to evaluate overseas literature on pavement deterioration prediction models with
the aim of identifying models possibly applicable to the national roads of South
Africa. Only deterioration models developed from the deterioration results of inservice
pavements under a normal traffic spectrum were evaluated. Models
developed from accelerated testing were avoided since these models virtually
eliminated long·term effects (these are primarily environmental but also include
effects of the rest periods between loads), and that the unrepresentative traffic
loading regimes can distort the behaviour of the pavement materials, which is
often stress dependent. Models developed from the following studies were
evaluated: • AASHO Road Test
• The Kenya study
• Brazil-UNDP study (HDM-ill models)
• Texas study
Of all the above models studied that were developed from major studies it was
concluded that the incremental models developed during the Brazil study, were
the most appropriate for further evaluation under South African conditions. A
sensitivity analysis was conducted on the HDM-III models to evaluate their
sensitivity to changes in the different parameters comprising each model. The
results obtained from the sensitivity analysis indicate that the incremental
roughness prediction model incorporated into the HDM-III model tends to be
insensitive to changes in most parameters. Accuracy ranges for input data were,
however, also identified for parameters which indicated an increase in
sensitivity in certain ranges.
The local applicability of the HDM-III deterioration models were finally
evaluated by comparing HDM-III model predictions with the actually observed
deterioration values of a selected number of national road pavement sections. To
enable the above comparison, a validation procedure had to be developed
according to which the format of existing data could be transformed to that
required by the HDM-ill model, as well as additional information be calculated.
From the comparison it was concluded that the HDM-III models are capable of
accurately predicting the observed deterioration on South African national
roads, but that for most models calibration is needed for local conditions.
Guidelines regarding recommended calibration factor ranges for the different
HDM-ill models are given.
Finally it is recommended that the HDM-III models should be considered for
incorporation into a balanced expenditure programme for the national roads of
Dissertation (MEng)--University of Pretoria, 1993.