Calculation method for permanent deformation of unbound pavement materials
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Insinööritieteiden ja arkkitehtuurin tiedekunta |
Doctoral thesis (article-based)
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Date
2009
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Language
en
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Verkkokirja (4232 KB, 91 s.)
Series
VTT publications,
702
Abstract
An analytical-mechanistic 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 full-scale 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 elasto-plastic model. The stress distribution studies of traffic load showed that it is very important to calculate stresses in pavements with an elasto-plastic 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 °C and 20 to 25% at +25 °C compared to rut depths at +5 °C due to the changes in the stiffness of the bound layer. The unloading-reloading 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.Description
Keywords
permanent deformations, rutting, unbound pavement material, pavement design, stress distribution
Other note
Parts
- [Publication 1]: Korkiala-Tanttu, L. and Laaksonen, R. 2003. Permanent deformations of unbound materials of road pavement in accelerated pavement tests. Proceedings of the 13th European Conference on Soil Mechanics and Geotechnical Engineering (ECSMGE 2003). Prague, Vol. 2, The Czech Geotechnical Society CICE, Prague. Editors: Vaníček, I., Barvínek, R., Boháč, J., Jettmar, J., Jirásko, D. and Salák, J. Pp. 665-670. © 2003 Czech Geotechnical Society. By permission.
- [Publication 2]: Korkiala-Tanttu, L. and Laaksonen, R. 2004. Modelling of the stress state and deformations of APT tests. Proceedings of the 2nd International Conference on Accelerated Pavement Testing. September 26.9.-29.9.2004, Minneapolis, Minnesota, CD-rom proceedings. Editor: Worel, B. 22 p. © 2004 University of Minnesota. By permission.
- [Publication 3]: Korkiala-Tanttu, L. and Dawson, A. 2008. Effects of side slope on low-volume road pavement performance: a full-scale assessment. Canadian Geotechnical Journal, NRC Research Press, Ottawa, Vol. 45, June 2008, pp. 853-866.
- [Publication 4]: Korkiala-Tanttu, L. and Dawson, A. 2007. Relating full-scale pavement rutting to laboratory permanent deformation testing. International Journal of Pavement Engineering, Taylor & Francis, Spon Press, Abingdon, Vol. 8, Issue 1, pp. 19-28.
- [Publication 5]: Korkiala-Tanttu, L. 2005. A new material model for permanent deformations in pavements. Proceedings of the 7th International Conference on the Bearing Capacity of Roads, Railways and Airfields (BCRA 2005). Trondheim 27.6.-29.6.2005, CD-rom proceedings, Publisher Ny Media AS, Oslo. Editor: Horvli, I. 10 p. © 2005 Ny Media AS. By permission.
- [Publication 6]: Korkiala-Tanttu, L. 2007. Speed and reloading effects on pavement rutting. Proceedings of the Institution of Civil Engineers, Geotechnical Engineering, Thomas Telford Journals, Vol. 160, July 2007, Issue GE3. Pp. 123-127. © 2007 Institution of Civil Engineers (ICE). By permission.
- [Publication 7]: Korkiala-Tanttu, L. 2008. Stress studies for permanent deformation calculations. Advances in Transportation Geotechnics. Proceedings of the 1st International Conference on Transportation Geotechnics. Nottingham 25.8.-27.8.2008, CRC Press, London. Editors: Ellis, E., Yu, H.S., McDowell, G., Dawson, A. and Thom, N. Pp. 201-206. © 2008 Taylor & Francis. By permission.
- [Errata file]: Errata of publications 1, 5 and 7