Analysis of Permanent Deformation in Flexible Pavements Built with Various Subgrade Soils at Various Moisture Conditions

To develop subgrade failure criteria and performance prediction models that consider the subgrade soil type and moisture condition, 12 sets of full-scale flexible pavement test sections were built inside the Frost Effects Research Facility of the U.S. Army Corps of Engineers. The pavement materials and layer thickness were kept constant, but the subgrade soil type and moisture condition varied from test section to test section. The test sections were subjected to accelerate traffic by means of a heavy vehicle simulator. Sensors were embedded in the test sections to measure deformation and stress. Although sensors existed in the vertical, longitudinal, and transversal directions, only vertical results are included in this paper owing to space limitations. Surface rutting was monitored by means of a laser profilometer. The temperature was artificially kept constant at room temperature. The subgrade soil moisture was kept constant during the testing by means of a closed basin system. Although intuitively, one can expect moisture above the conventional “optimum” to play a weakening role, the experimental data suggest that this is not always the case. The experimental data support the formulation of quantitative relationships between subgrade moisture content and performance for each of several subgrade soil types. Consideration of these moisture effects for various subgrade soils can be used to improve the permanent deformation models currently built into the NCHRP 1-37A Design Guide. This paper contains an analysis of permanent deformation based on experimental results. Other papers are planned to cover other aspects, such as stress–strain relationships, load-damage, and performance models.