Plastic deformation potentials of sandy clay from repeated load triaxial test

Design and analysis of flexible pavement systems depend on soil layer characterization, traffic loads and number of passes. Currently, AASHTO uses resilient characteristics of subsoils to characterize and determine the structural support of each layer and then designs the layer thickness. Resilient properties are used in the characterization since they are assumed to account for plastic deformation of subsoils. Hence, there is an important research need to evaluate the plastic deformation behaviors of subsoils. A research study was initiated to establish a test procedure to measure plastic strain potentials of subgrade soils using a repeated load triaxial device. The test was performed for 10,000 cycles in order to monitor the plastic strains. This paper presents these test results that were conducted on sandy clay. Effects of compaction moisture content, confining pressure and deviatoric stresses on the plastic strains of soil are addressed. A case study was used to explain the significance of plastic deformation measurements of soils in their overall contribution to rutting.