Abstract
An analyticalmechanistic method for the calculation of
permanent deformations of pavements has been developed at
the Technical Research Centre of Finland (VTT) over some
years by the author. The calculation method is needed in
the analytical design procedure of pavements. This
research concentrated on the calculation method for
permanent deformations in unbound pavement materials. The
calculation method was generated based on the results of
fullscale accelerated pavement tests along with the
complementary laboratory tests together with finite
element calculations.
The objective was to develop a relatively simple material
model for unbound materials, which is an analytical,
nonlinear elastoplastic model. The stress distribution
studies of traffic load showed that it is very important
to calculate stresses in pavements with an elastoplastic
material model to avoid false tensile stresses in unbound
materials, especially when the asphalt layers are thin.
The new material deformation model can take into account
the amount of the loading, the number of vehicle or wheel
passes, the deformation capacity of the material and its
stress state. The strains in each layer and subgrade are
calculated and converted to the vertical deformations and
then summed to obtain the total rutting. The method was
verified against two Finnish accelerated pavement tests.
The results indicated that the material model gave
tolerable results for the relatively high load levels
used in these Heavy Vehicle Simulator (HVS) tests as the
relative error was around ± 30%. For the structures with
thicker bound layers and therefore lower stress state in
the unbound layers, the method gave more reliable
results.
The material parameters have been defined only for the
most common Finnish unbound materials in a few basic
situations. The wider use of the method requires material
parameter definitions for a larger range of materials.
However, even in the current form the method can be
applied in a relatively reliable way to compare the
sensitivity of different structures against rutting.
The most important factors affecting rutting were studied
to find a method to include their effect on the
calculation method. These factors were loading rate,
stress history, temperature and the geometry of the road
embankment. The modelled examples proved that the most
important factor of rate effect is the change in stress
state due to the change in the resilient properties of
bound layers, while the rate effects on the unbound
material itself has a smaller role. The accelerated
pavement test proved that rut depth depends greatly on
the temperature: the rut depth grows from 10% to 15% at
+10 ºC and 20 to 25% at +25 ºC compared to rut depths at
+5 ºC due to the changes in the stiffness of the bound
layer. The unloadingreloading cycles have only a slight
effect on the permanent deformation. The introduced
geometric factor describes an average, structurally
independent, increase in the rate of rutting, which
depends on the steepness of the side slope and on the
distance to the edge of the structure.
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Supervisors/Advisors 

Award date  30 Jan 2009 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9789513871352 
Electronic ISBNs  9789513871369 
Publication status  Published  2008 
MoE publication type  G5 Doctoral dissertation (article) 
Keywords
 permanent deformations
 rutting
 unbound pavement material
 pavement design
 stress distribution
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KorkialaTanttu, L. (2008). Calculation method for permanent deformation of unbound pavement materials: Dissertation. VTT Technical Research Centre of Finland. http://www.vtt.fi/inf/pdf/publications/2008/P702.pdf