First level analysis report: comparative testing of HVS Mk IV+ and HVS Mk III on road D2388 near Cullinan

Abstract

After many years of owning and operating a Heavy Vehicle Simulator (HVS) Mk III, Gautrans acquired a HVS Mk IV+ in May 2002. In addition to the advanced features that this machine possesses in comparison to its predecessor, the HVS Mk IV+ also has certain operational advantages that will make it more efficient than the Mk III. The HVS Mk IV+ will be utilised in all future Accelerated Pavement Testing (APT) operations undertaken by Gautrans. The differences between the two machines could, however, result in variations in pavement response and test results. Based on this concern and in an effort to ensure uniformity throughout APT with the HVS, a comparative testing project was initiated to compare the effect of the two machines on pavement response. Differences in the pavement response induced by the HVS Mk III and HVS Mk IV+ may be caused by differences in the trafficking speed of the machines (loading frequency), differences in the total load applied by the machines and differences in the contact stresses applied by different tyre brands and tyre widths used on the two machines. An attempt was made to eliminate the effect of total load by developing total load calibration curves for the two HVSs prior to comparative testing. The procedure followed during the comparative testing was to identify two test sections for testing. These test sections were subjected to trafficking by each of the HVSs until elastic and plastic response trends could be established for both test sections. The machines were then swapped and trafficking continued until the new elastic and plastic pavement responses trends could confidently be compared to the original response trends. Small but consistent changes in the elastic deflection were observed when the machines where swapped but these changes were too small to influence the interpretation of the elastic response results under normal testing conditions. The changes in the permanent deformation response that were observed when the machines were swapped are of greater concern and could lead to different conclusions regarding the bearing capacity of the test pavement. It is, however, suspected that the observed differences in pavement response could be caused by differences in the applied total load and contact stresses at the operational trafficking speeds of the machines. Further work is recommended to investigate this.