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, the AASHTO uses resilient characteristics of subsoils to characterize and determine the structural support of each layer and then design the layer thickness. Resilient properties are used in the characterization since they are assumed to account for plastic deformation of subsoils. This assumption is known to provide misleading characterizations in mixed soils. 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. This test was performed for 10,000 cycles to monitor the plastic strains. This paper presents these test results conducted on sandy clay. Effects of compaction moisture content, confining pressure and deviatoric stresses on the plastic strains of soils are addressed. A case study was used to explain the significance of plastic deformation measurements of soils in their overall contribution to rutting.