Monitoring pavement response during spring thaw and validation of the thaw weakening index

Seasonal variation in pavement response is considered to be a major factor affecting pavement performance. Several studies have concluded that in cold climates, most of the pavement damage by fatigue and permanent deformation can be associated with the loss of bearing capacity during spring thaw. The understanding of the bearing capacity loss phenomena needs to be improved and pavement design methodologies dealing specifically with the problem need to be developed. The Quebec Ministry of transportation, in collaboration with the Laboratoire central des ponts et chaussées (LCPC, France) and Laval University, has undertaken a major research project based on the monitoring of instrumented test sections. Four heavily circulated test sections were constructed and instrumented. Pavement instrumentation includes thermistors, moisture sensors, frost gages, piezometers and heave gauges. Several techniques were used to monitor pavement response during spring. One of the outcomes of the project is the development of a new mechanistic index likely to help predicting the bearing capacity loss during spring thaw in specific climatic and soil conditions. The index is based on the three important factors of thaw weakening: the quantity of ice accumulated in the soil by frost action, the rate of thaw and the rate of thaw consolidation. The new index was found to correlate well with measured loss of bearing capacity at several test sites.