The pavement was modelled in 3D, considering visco-elastic behaviour for the bituminous material, and the non-linear elastic Boyce model (Eq. 9.10) for the unbound granular material and the soil. The material parameters for the bituminous layer were determined from complex modulus tests and the in-situ temperature of the bituminous layer was taken into account in the modelling. The parameters for the unbound granular material (UGM) and for the subgrade were determined from repeated load triaxial tests. For the UGM, tests were performed at 3 different water contents: 2.3%, 3.8% and 4.8%, corresponding to the water content variations observed on the site.
11.4.5.1 Modelling of the Pavement Response for Different Water Contents
A series of calculations was performed for the 3 load levels and the 3 moisture contents of the UGM at a constant loading speed of 68 km/h.
Figures 11.12 and 11.13 show comparisons between measured and calculated maximum longitudinal strains at the bottom of the bituminous layer (exx BB), and maximum vertical strains at the top of the UGM layer (ezz GNT), for the 3 load levels. The results show that:
The model predicts relatively well the strains in the granular layer (ezz GNT), and their non-linear increase with load level. The strains in the bituminous layer (exx BB) are slightly over-predicted.
The water content of the granular layer has a strong influence on the vertical strains in the UGM layer. Increasing w from 2.3 to 4.8% increases the strains by about 60%. The calculations with w = 3.8% lead to the best predictions, close to the mean of the experimental measurements.
The calculations with the 3 water contents led to a range of variation of the vertical strains in the UGM layer similar to the scatter of the experimental measurements.
Figures 11.14, 11.15 and 11.16 present additional examples of prediction of signals of longitudinal and transversal strains at the bottom of the bituminous layer
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Fig. 11.14 Comparison of experimental and predicted longitudinal strain exx at the bottom of the bituminous layer — load 65 kN |
(exx and eyy), and vertical strains at the top of the UGM layer (ezz), for the load of 65kN. The results show that CVCR (with w = 3.8% for the UGM) predicts well the strain signals (strain variations when the load moves in the x direction). The experimental curves of exx and eyy at the bottom of the bituminous concrete are non-symmetrical, due to the viscosity of the material, and this is well predicted by the visco-elastic model.
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Fig. 11.15 Comparison of experimental and predicted transversal strain eyy at the bottom of the bituminous layer — load 65 kN |
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x (m) -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 Fig. 11.16 Comparison of experimental and predicted vertical strain ezz at the top of the granular layer — load 65 kN |
