Rutting of Thin Pavements: Full-Scale Study

Since 1992, the Federal University of Rio Grande do Sul, along with the roads department of the same Brazilian state, has undertaken comprehensive research on weathered basalts, with the purpose of reducing the cost of low-volume pavements. Laboratory studies have led to a criterion (on the basis of the point load test) used to select deposits of these intensely fractured rocks. A traffic simulator was designed and built, and a pavement test facility was constructed on the university campus. A study was done of rutting of thin pavements on which weathered basalts were used as base layers. The traffic simulator applied more than 267,000 axle loads, ranging from 82 to 130 kN, on five full-scale test sections. Two different weathered basalts and three base thicknesses were used. A postmortem evaluation revealed that the base layer contributed the most to rutting. The axle load applications caused the pavement structure to settle and consolidate. A total of 4,148 measurements of rut depth, made at intervals, provided a statistically significant data set. Rutting evolution was shown to depend not only on traffic characteristics but also on pavement structure. With consideration of rutting as a major failure cause in thin pavements and a rut depth of 25 mm as a terminal criterion, load equivalence factors were calculated by means of a reliability analysis.