Hysteresis Model for Water Retention Characteristics of Water-Absorbing Polymer-Amended Soils

Abstract

Water absorbing polymers (WAPs) are gaining attention in the field of geotechnical engineering, with application to bioengineered slopes, vegetation growth on landfill covers, and maintenance of green infrastructure in arid climate regions. WAP-amended soil is often exposed to alternate drying–wetting cycles, which influence its water retention characteristics. Determining the hysteresis in water retention characteristics of WAP-amended soils is crucial to evaluate their hydraulic performance with time. The present study proposes a methodology to measure the hysteresis in soil–water retention curve (SWRC) of WAP-amended soils subjected to alternate drying–wetting cycles. For this purpose, the drying–wetting SWRC of three different textured soils (sand, silt loam, and clay loam) were determined for varying WAP concentrations (0.1%, 0.2%, and 0.4% on weight-by-weight basis). Fourier transform infrared (FTIR) spectroscopy was used to confirm degradation in the polymer chain of the WAPs with the progressive wetting–drying cycles, which significantly affected the hysteresis phenomenon. A predictive model was proposed to estimate the wetting SWRC from the drying SWRC for WAP-amended soils, which is valid until the complete degradation of the WAPs. The proposed model was validated for two consecutive drying–wetting cycles for the selected soils with varying WAP concentrations, which showed its effectiveness for predicting hysteresis behavior in SWRC of WAP-amended soils. Further, the degree of hysteresis in SWRC of WAP-amended soil was quantified after each drying–wetting cycle. The experimental results revealed that the presence of WAP and its degradation with time significantly increased the degree of hysteresis in SWRC.