1 Department of Planning, Technical University of Denmark2 Department of Transport, Technical University of Denmark3 Danish Road Directorate
Preliminary Test Pavement Danish Road Testing Machine
Main conclusions: 1) The Asphalt Strain Gauges (ASG), the Soil Deformation Transducers (SDT) and the Soil Pressure Cells (SPC) performed well during the experiment, but the SPCs need frequent in situ calibration. A different installation procedure for the SPCs should be considered. Due to the variability of the soil more instruments (than two) are needed for each response value to be determined. 2) Strains measured using the emu coils did not have a satisfactory degree of accuracy. Laboratory tests showed the Kulite pressure cells to be dependent upon loading history and soil stiffness. For this reason the cells were not used in the RTM experiment. The volumetric moisture content recorded by the VITEL moisture probes did not appear to be reliable. 3) Linear elastic theory did not give a satisfactory agreement with measured stresses and strains. The measured vertical strains could be several times larger than the theoretical values. Elsym5 seems to produce incorrect deflections in some cases. 4) Satisfactory agreement between measured and theoretical stresses and strains could be obtained using the Finite Element Method and appropriate non-linear relationships for the moduli of the unbound materials. 5) The variation of stresses and strains with distance from the load was found to be in very good agreement with Boussinesgs equations, with the exception of the horizontal stress. The relationship between the depth used with Boussinesq's equations the the actual depth needs further study. 6) The subgrade showed thixotropyc behavior with strains increasing with the number of load repetitions and decreasing after a rest period. This behavior was only observed under the wheel load, not under the FWD. 7) Existing design criteria for subgrades appear to be reasonable when used with strains calculated using linear elastic theory and moduli determined from FWD tests, but ar much too conservative if used with measured strains. 8) Plastic strain in the subgrade, surface rutting and roughness could all be related to the measured resilient strain at the top of the subgrade, with damage being proportional to the load raised to a power between 6.23 and 6.67. These relationships can be used to calculate the pavement condition after a given number of loads or to determine the permissible number of loads for a given terminal condition of the pavement. For surface rutting and roughness the contribution from the individual layers could not be established.