LAYERED SYSTEM PERFORMANCE EVALUATION PHASE II FINAL REPORT

Research was undertaken to study the behavior of layered systems used as part of transportation structures. Particular emphasis is given to the "tension" zone in the bottom portion of upper granular layers overlying less stiff layers. The research has included layered system experiments, special computer controlled triaxial tests, and analysis. This report presents the results of Phase II. In Phase I the experimental apparatus was constructed and test techniques established, a strain path triaxial test program was developed, preliminary experiments were conducted, and a review of past research was completed. In Phase II, experiments were conducted with a layer of sand over clay. Both stress and strain measurements were made in the soil as a result of repeated surface loading. Strain path triaxial tests were conducted to help interpret the tank strains in terms of stresses. The trends were also evaluated with theoretical analysis using a special constitutive model for sand. The development of horizontal residual stresses which control the cumulative deformations under repeated load was clearly demonstrated.