Accelerated load testing of pavements was done with the HVS-NORDIC at VTI in Sweden in 1998 (Wiman, 2001). Figure 8.5 shows the rut depth measurements for a weak pavement comprising a 49mm thick asphalt layer over a bitumen stabilised granular base of thickness 89mm over a sand subgrade 2.5 m thick (mean thicknesses).
After 500 000 passes the increase in rut depth was constant and only 0.88 mm/100 000 passes. Then it was decided to increase the test load from 60-80 kN
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Passes 0 500 000 1 000 000 1 500 000 2 000 000 2 500 000 Fig. 8.5 Rut depth propagation rates during test SE01. Figure courtesy L. Wiman, reproduced by permission of VTI |
and the tyre pressure from 800 to 1000 kPa. The rut propagation increased but only to 1.03 mm/100 000 passes. The next step was to weakening the sub grade by adding water to the sand to bring the water table to a level 300 mm below the surface of the sub grade — the highest level permitted in the Swedish specifications when constructing new pavements. The test load was at the same time reset to 60 kN and a tyre pressure of 800 kPa. Now the rut propagation increased to 4.16 mm/100 000 passes and the first cracks could be seen at the pavement surface.
