Descriptive fault trees for structural pavement failure mechanisms

Unplanned structural road pavement failures may increase maintenance expenditure for road authorities from that estimated in budgets. To deal with this effectively, road asset managers who are faced with the complex task of forecasting and planning maintenance with fixed and constrained budgets, or operating road networks with high risk profiles, need to understand the factors affecting road pavement failure. However, this is often a difficult task due to the interaction of failure factors and associated failure mechanisms. Several industries utilise approaches, such as fault trees, for infrastructure systems which utilise an understanding of failure modes to better understand the causes of asset failure. This paper explores the use of such an approach for road pavements. A methodology is described which can be used by asset managers to correctly diagnose the mode(s) of pavement failure and the associated cause(s). Three fault trees for rutting, load associated fatigue cracking, and shear failure are developed and their effectiveness is demonstrated through their use in both the initial stages of development and interpretation of the outputs generated by a computer model developed to predict road pavement failure. A case study using New Zealand road network data is used to demonstrate the process.