Rut Accumulation and Power Law Models for Low-Volume Pavements Under Mixed Traffic

The fourth-power law has been used for more than 40 years to assist the modeling of the damage that accumulates in pavements due to different traffic load levels and differing numbers of load applications. This paper studies the applicability and the limits of applicability of this law to typical low-volume road pavements with no or only thin seals that obtain their structural performance primarily from the aggregate base (or equivalent) layer and for which pavements' deterioration is overwhelmingly due to rutting. After behavior of unbound granular pavement materials has been reviewed, data from four sources is used to show that it is sometimes impossible to model real pavement response by any power relationship. Furthermore, power values, even when usable, are highly variable and can vary widely with construction material and with distress criteria. It is shown that, even when a power law is a reasonable way of interpreting data, a value for the law of 4 is not. Some suggestions are given for alternative approaches and adaptations.