Cracking Mechanism of Flexible Pavements

The paper deals with the cracking of flexible pavements caused by shrinkage due to drying of the subgrade. A cracking mechanism in pavements is proposed, based on the principle that cracks first appear in the subgrade and are afterwards reflected through the asphaltic layer. Subgrade cracks form under the combined action of the shrinkage by drying and the frictional resistance produced by the granular courses, i.e., restrained shrinkage. A model simulating part of the site conditions is analyzed by the finite element method; results of the analysis are in satisfactory agreement with the test findings. The analysis is also applied to the cracking mechanism at the site. The principal conclusions derived from the results are: (1) Cracking may occur in the subgrade; and (2) a 90-cm thick pavement is able to prevent reflection of cracking. Two cases of cracking, a covered shoulder and a runway, are described. Both cases support the hypothesis of crack reflection.