DEVELOPMENT OF A SUBGRADE FAILURE CRITERIA USING ACCELERATED PAVEMENT TESTING

Current subgrade failure criteria are limited and the one most used in mechanistic pavement design is based on test data collected from the AASHO Road Tests in the late fifties. The strain criterion was based on a single subgrade soil (CL), on theoretical strains calculated on top of the subgrade, and was based on the subgrade modulus estimated from the California Bearing Ratio. With the advent of the new AASHTO mechanistic design guide, it is important to quantify the impact of soil type and moisture content on the subgrade failure criterion. Accelerated pavement testing was conducted on full-scale test sections. The test sections consisted of several subgrade types, of which one was a SM soil. The test subgrades were constructed at 2 moisture contents. The sections were instrumented with pressure and strain, temperature and moisture sensors and subjected to accelerated loading. Testing was terminated when the surface rut depth reached or exceeded 12.5 mm. The results indicate that the subgrade type and moisture content has a significant influence on the strain based failure criterion. Failure criteria (strain) as a function of soil type and moisture content were developed and presented in this paper.