| Recycled granular waste materials (RGWMs) including fly ash from thermal utility plants are generated in large quantities worldwide. Some of these materials are composed of metastable minerals and metals that are considered to be hazardous. Due to availability of few data on long-term field performance and stress-strain behavior, bulk of the material is still being disposed in landfills. In this study, extensive laboratory experiments were carried out on fly ash to characterize both its short and long-term stress-strain-strength behavior under triaxial stress, hydraulic characteristics, and leachability under various stress regimes.; The results of this study indicate that fresh fly ash sheared at confining stresses in excess of 50 kPa exhibits volumetric contraction, build-up positive pore pressure, and deviates from the critical state theory. Volumetric contraction is largely due to fracture and collapse of crushable particles present in the material. However, as the material ages, its stress-strain characteristics and pore pressure behavior are similar to those of dense sand and overconsolidated clay materials. A constitutive relationship that captures the strain-softening behavior of the fresh fly ash material used in this study was developed. Effects of age, loading regimes, and placement density on leaching characteristics are quite complex and differ for most of the metals analyzed. While leaching of Se is almost independent of the placement density and decreases continuously with increase in confining stress, Cu and Zn are more leachable in dense state and at low (35 kPa) and high (420 kPa) confining stresses. |
