There have been a number of high-profile early failures in New Zealand pavements (rut depths greater than 20mm observed early in the pavement life) associated with ‘greenfield’ pavements (pavements not subjected to traffic during construction). It is uncertain if the rutting was due to poor construction control, difficulties of measuring density of thick layers or a function of lack of traffic on the pavement. In response, a research project was initiated to investigate in the NZ Transport Agency’s accelerated pavement testing facility (CAPTIF) the effect of constructing the basecourse and sub-base to a range of densities (88% to 95% of maximum dry density).
In addition to the CAPTIF trial a more theoretical analysis consisting of comparing the theoretical stress and strain distribution under a vibratory roller and a standard heavy vehicle was performed.
The conclusion of the research was that by using conventional New Zealand construction techniques and specifications some post-construction deformation of greenfield pavements appears to be inevitable. The permanent strain developed will manifest itself into a larger rut depth as the granular thickness increases. However, the rut depth should not approach the levels (20mm) that prompted the initiation of this research.