A Study on the Behavior of Pond Ash in Unsaturated Conditions Through WRCC

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Pond ash is a residue obtained from the combustion of pulverized coal in Thermal power plants. Out of the total production of pond ash, only a small quantity of ash is utilized and the remaining unutilized pond ash is deposited as a waste material covering several hectares of land. Usefulness of coal (Pond) ash has been explored in various geotechnical and geoenvironmental practices like the construction of ash dyke, road and railway embankment, landfill liners, etc. which requires detailed knowledge of geotechnical and unsaturated behavior of pond ash. The understanding of the engineering behavior of unsaturated soil is totally dependent on the water retention characteristic curve (WRCC) which is a graphical relationship between volumetric water content and soil suction. In this paper, the geotechnical characterization and water retention characteristic curves of pond ash have been studied. WRCC has been drawn experimentally using Fredlund device based upon the pressure plate technique for wetting and drying cycles, both. Further, an investigation was carried out to study WRCC hysteresis of Pond ash. There exists considerable hysteresis in drying and wetting curves of pond ash samples which indicates a significant difference in behavior between drying and wetting phases. The different WRCC models were used to fit the experimental WRCC data. The measured WRCC match satisfactorily with predicted WRCC using Fredlund and Xing equation whereas there is an upward shift in the WRCC curve derived using Van Genuchten equation as compared to experimental WRCC. Since the direct measurement of unsaturated hydraulic conductivity is difficult to obtain in engineering practices, the unsaturated hydraulic conductivity function is predicted using measured WRCC as the input parameter using SEEP/W software. The behavior of pond ash was also compared with the results obtained for natural sand as a reference material.