Using Repeated-Load Triaxial Tests to Evaluate Plastic Strain Potentials in Subgrade Soils (05-2619)
Anand J. Puppala, University of Texas, Arlington
Suppakit Chomtid, University of Texas, Arlington
Venkata Bhadriraju, The University of Texas at Arlington

Design and analysis of flexible pavement systems depend on soil layer characterization, traffic loads and number of passes. Currently, the AASHTO design method for flexible pavements uses resilient characteristics of subsoils to characterize and determine the structural support of each layer to design the thickness of the layer. This property, however, does not fully account for the plastic strain or rutting potentials of subsoils as is the case in which silt and mixed soils undergo high plastic deformations though display high resilient properties. A research study was initiated to establish a test procedure to measure plastic strain potentials of subgrade soils using a repeated load triaxial device. Laboratory compacted soil specimens were subjected to a deviatoric repeated load, as a percentage of static deviatoric load at unconsolidated undrained conditions, for 10,000 cycles. The plastic strains were monitored during test cycles and the accumulated plastic deformations were determined. This paper presents both the test procedure and test results conducted on two types of soils, a coarse sand and silty clay. Effects of compaction moisture content and dry unit weight, confining pressure and deviatoric stresses on the plastic strains of both soils are addressed. Improvements to the subgrade characterization when utilizing additional plastic deformation data are also provided.