Prediction of Hysteresis in the Water Retention Curve for the Fly Ash‐Based Hydrogel‐Amended Soils

ABSTRACT Climate‐induced drying–wetting cycles have severe impacts on different soil infrastructures and agricultural productivity in semi‐arid regions. Owing to their hydrophilic nature, superabsorbent hydrogels are gaining significant attention for reducing the negative influence of climate change on soil properties. Knowledge of the hysteretic behaviour of the water retention properties of hydrogel‐amended soils is needed to understand their long‐term hydraulic performance. This study examined the drying‐wetting soil–water retention curve (SWRC) of a fly ash‐based hydrogel (FAH) amended with three different textured soils for two consecutive cycles. The leachability of toxic heavy metals from the developed FAH was evaluated via the toxicity characteristics leaching procedure (TCLP). The efficacy of a predictive hysteresis model was investigated for estimating the wetting SWRC of FAH‐amended soils from the measured drying SWRC. The inclusion of FAH particles significantly improved the SWRC of the soils used in the lower suction range ( Ψ < 100 kPa). The hysteresis loop in the SWRC increased with increasing FAH content for both drying and wetting cycles. Moreover, width of the hysteresis loop decreases with the increasing number of cycles due to the degradation of the FAH polymer chain during the soil‐FAH‐pore water interaction. The predictive hysteresis model successfully captured this decrease in the hysteresis loop with increasing drying–wetting cycles for the FAH‐amended soils.