Rut depth prediction of granular pavements using the repeated loadtriaxial apparatus and application in New Zealand specifications forgranular materials

摘要

The rutting of granular pavements was studied by examining the permanent deformationbehaviour of granular and subgrade materials used in a Northern Ireland (UK) pavement field trial and accel-erated pavement tests at CAPTIF (Transit New Zealand's test track) located in Christchurch New Zealand.Repeated Load Triaxial (RLT) tests at many different combinations of confining stress and vertical cyclic stressfor 50,000 loading cycles were conducted on the granular and subgrade materials. The aim of the RLT testswas to derive relationships between permanent strain and stress level. These relationships were later used infinite element models to predict rutting behaviour and magnitude for the pavements tested in Northern Irelandand the CAPTIF test track. Predicted rutting behaviour and magnitude were compared to actual rut depth mea-surements during full scale pavement tests to validate the methods used. It was found that the trend (long termtangential rate of rutting) in rut depth progression was accurately predicted for 11 out of the 17 full scalepavement tests, while the magnitude of rut depth predicted for these 11 tests was within 3mm of the mea-sured values. Three of the poorly predicted test sections were still reasonably predicted while the other threepoor predictions were considered outliers due to differences in moisture content between RLT tests and in thefield. As a result of the success of this predictive method of assessing rutting in granular materials TransitNew Zealand undertook a three year study to implement a RLT test into specifications for selecting road baseaggregate. Eight New Zealand aggregates of known performance in the road were selected for RLT testingand associated rut depth prediction to confirm the RLT test can predict performance for a range of aggregatetypes. Results were positive and the RLT test was implemented into Transit New Zealand's specification forselecting basecourse aggregate. It is expected the benefits of this new test will reduce the number of earlypavement rutting failures and allow the use of alternative materials such as local quarry overburden materialmodified with cement which show equivalent performance in the RLT test to traditional high quality granularmaterials.