Influence of subgrade type and moisture content on failure criteria

Accelerated pavement testing was conducted at the U.S. Army Cold Regions Research and Engineering Laboratory on full-scale test sections. The test sections had a common geometry, but consisted of different subgrade types and moisture contents. The sections were instrumented with pressure, strain, temperature, and moisture sensors. The sections were subjected to accelerated loading, and stress and strain measurements were made periodically. Testing was terminated when the surface rut depth reached or exceeded 12.7 mm. The project is not yet completed. We have completed testing of two of the subgrade soils and are in the process of testing the third soil. A fourth soil will be tested in the near future. With the added data it will be possible to investigate other failure criteria in addition to vertical strain, to determine which one best predicts subgrade shear deformation. To date the results indicate that the subgrade type and moisture content have a significant influence on the strain-based failure criterion. Failure criteria (vertical compressive strain) as a function of soil type and moisture content were developed and are presented in this paper.