Calculation method for permanent deformation of …

1 VTT PUBLICATIONS 702 Calculation method for permanent deformation of unbound Korkiala-TanttuESPOO 2008 ESPOO 2008 ESPOO 2008 ESPOO 2008 ESPOO 2008 VTT PUBLICATIONS 702 Leena Korkiala-TanttuCalculation method for permanentdeformation of unbound pavementmaterialsAn analytical-mechanistic method for the Calculation of permanentdeformations in unbound pavement layers and subgrade has beendeveloped at VTT. The Calculation method is needed in the analyticaldesign procedure of pavements. The Calculation method was generatedbased on the test results of accelerated pavement tests along with thecomplementary laboratory tests made in developed Calculation method for unbound materials was basedon an analytical, nonlinear elasto-plastic model.

2 The stress state of thestructure was modelled using finite element method and non-linearelasto-plastic material model. The deformations were then calculated foreach layer from the number of passes, the bearing capacity of thematerial and its stress state. The saturation and compaction degrees weretaken into account by varying material parameters. So far only the basicmaterial parameters are known, thus more material studies are method was tested against two Finnish accelerated pavementtests. The results indicated that the material model gave tolerable resultsfor the high load levels. For the lower load levels the method gave morereliable results. The method can also be applied to the comparison of thesensitivity of different structures against 978-951-38-7135-2 (soft back ed.)

3 ISBN 978-951-38-7136-9 (URL: )ISSN 1235-0621 (soft back ed.)ISSN 1455-0849 (URL: )Julkaisu on saatavanaPublikationen distribueras avThis publication is available fromVTTVTTVTTPL 1000PB Box 100002044 VTT02044 VTTFI-02044 VTT, FinlandPuh. 020 722 4520 Tel. 020 722 4520 Phone internat. + 358 20 722 4520 VTT PUBLICATIONS 702 Calculation method for permanent deformation of unbound pavement materials Leena Korkiala-Tanttu Dissertation for the degree of Doctor of Science in Technology (Doctor of Philosophy) to be presented with due permission of the Department of Civil and Environmental Engineering, Helsinki University of Technology for public examination and debate in Auditorium M1 at Helsinki University of Technology (Espoo, Finland) on the 30th of January, 2009, at 12 noon.

4 ISBN 978-951-38-7135-2 (soft back ed.) ISSN 1235-0621 (soft back ed.) ISBN 978-951-38-7136-9 (URL: ) ISSN 1455-0849 (URL: ) Copyright VTT 2008 JULKAISIJA UTGIVARE PUBLISHER VTT, Vuorimiehentie 5, PL 1000, 02044 VTT puh. vaihde 020 722 111, faksi 020 722 7001 VTT, Bergsmansv gen 5, PB 1000, 02044 VTT tel. v xel 020 722 111, fax 020 722 7001 VTT Technical Research Centre of Finland, Vuorimiehentie 5, Box 1000, FI-02044 VTT, Finland phone internat. +358 20 722 111, fax +358 20 722 7001 Technical editing Maini Manninen Edita Prima Oy, Helsinki 2008 3 Korkiala-Tanttu, Leena. Calculation method for permanent deformation of unbound pavement materials [Tierakenteen sitomattomien materiaalien pysyvien muodonmuutosten laskentamenetelm ].

5 Espoo 2008. VTT Publications 702. 92 p. + app. 84 p. Keywords permanent deformations, rutting, unbound pavement material, pavement design,stress distribution 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.

6 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.

7 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. 4 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.

8 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.

9 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. 5 Korkiala-Tanttu, Leena. Calculation method for permanent deformation of unbound pavementmaterials [Tierakenteen sitomattomien materiaalien pysyvien muodonmuutosten laskentamenetelm ]. Espoo 2008. VTT Publications 702. 92 s. + liitt. 84 s. Avainsanat permanent deformations, rutting, unbound pavement material, pavement design,stress distribution Tiivistelm Viime vuosina VTT:ll on kehitetty menetelm tien rakennekerrosten pysyvien muodonmuutoksien laskentaan.

10 Menetelm on osa p llysrakennekerrosten mi-toitusmenettely . Menetelm kehitettiin erityisesti sitomattomien rakenneker-rosten muodonmuutoksien laskemiseen ja sen kehitt misess hy dynnettiin sek t yden mittakaavan koetiekonetta ett laboratoriokokeiden tuloksia yhdess mallintamisen kanssa. Tavoitteena oli kehitt sitomattomien rakennekerrosten pysyvien muodon-muutosten laskentaan suhteellisen yksinkertainen materiaalimalli, joka on analyyttinen, ep lineaarinen ja elastoplastinen. Liikennekuormitusta mallinnettiin elementtimenetelm ll . Mallinnusten perusteella osoittautui, ett on oleellista mallintaa tien rakennekerrosten j nnitystila pysyvien muodonmuutosten laskentaa varten elasto-plastisilla menetelmill.