Australian flexible pavement design methodology

With the use of the design guide, flexible and rigid pavements can be designed. The flexible pavements may consist of asphalt, unbound, hydraulically bound or hydraulically bound/ unbound layers. 

In the analysis, pavement materials are considered to be homogeneous, elastic and isotropic, except for unbound granular materials and subgrades, which are considered to be anisotropic. 

Stress analysis is carried out by using a linear elastic model, such as the computer program CIRCLY (Mincad Systems 2009). 

The design criteria used are as follows the horizontal tensile strain at the bottom of the asphalt layer or of the HBMs and the vertical compressive strain at the top of the layer no consideration was given for the unbound aggregate layer. 

For the selection of the materials, it is recommended to also consider subsequent publications related to the manual (Austroads 2013a,b). The first is related to modified granular materials (unconfined compressive strength 2.0 MPa) and bound materials (hydraulically or bitumen bound) for base/sub-base course. The second is related to selected subgrade and lime-stabilised subgrade material. 

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However, in the Australian pavement design methodology for rigid pavements (Austroads 2012), the axle loads determined as in flexible pavement (using the equivalency law) are multiplied by a load safety factor (LSE). The ESP is related to project reliability, which varied from 80% to 97.5%. Eor a reliability of 95%, the LSE for an unreinforced slab is 1.3, while that for a doweled or continuously reinforced slab is 1.25. 

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