Surface Rut

Once the layer compression of each layer is determined, the total permanent deformation DP, can be calculated as the sum of permanent deformation in each individual layer using the following equation:

where d_p,i is the permanent deformation for layer i. The percent of wheelpath rutted, PWR, is then calculated using a transfer function similar to the one for cracking:

where           DP₅₀ is the critical permanent deformation correspond to 50% wheelpath having rutting failure, and

          b_rut is the shape parameter.

Similar to fatigue cracking, both critical permanent deformation and shape parameter are determined through field calibration, and each may depend on additional factors such as pavement structure type, climate condition, HMA layer thickness.