Application of Superabsorbent Polymer to Modify Soil Engineering Properties

Date

2023

Authors

Jafari, Elahe

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Abstract

Soil moisture content fluctuates considerably due to environmental changes, particularly in clay, which can undergo volume changes and loss of strength with increasing water content. The use of superabsorbent polymer (SAP) as an additive to maintain soil moisture stability is proposed in this study. SAP is non-toxic, vegetation-friendly, and inexpensive, making it suitable for numerous geotechnical applications. The first essay investigates the effect of SAP on the engineering properties of clay through compaction tests and direct shear tests on different ratios of SAP-soil mixtures. The results show that addition of SAP to clay increases the optimum water content of clay and decreases its maximum dry density. At the moistures lower than optimum water content, SAP slightly reduces the cohesion of SAP-soil mixtures while the friction angle remains nearly unchanged. However, both cohesion and friction angle of SAP-soil mixtures improve significantly by raising the SAP ratio in water contents higher than optimum water content. Addition of SAP to soil restricts shear strength fluctuations caused by moisture changes and enhances stability and consistency in the soil's dry density. The second essay establishes the soil-water characteristic curve (SWCC) for soil and different mixtures of soil with SAP to determine the impact of SAP on the suction potential of clay for the suction range of 0-20MPa. Comparing the resulted SWCC for soil and SAP-soil mixtures shows that saturated water holding capacity of clay improves by 860% by adding 2% SAP. When SAP is mixed with soil, it achieves only about 35% of its swelling potential due to the constraining properties of the soil structure, even when the mixture is fully saturated. Among the trained models to predict the suction potential of SAP-soil mixtures, mathematical polynomial interpolation and K-nearest-neighbors (KNN) techniques are shown to have the most accurate predictions based on the R-squared and mean squared error (MSE). In the third essay, an assessment is carried out to determine the Atterberg limits and swelling behavior of soil mixtures containing SAP under various loads. Moreover, this essay investigates the leaching and dissolution properties of SAP, as well as its long-term effectiveness in response to wetting-drying cycles in the field. The Atterberg tests revealed that as the ratio of SAP in the soil mixture increased, both the liquid limit (LL) and plastic limit (PL) rose. The plasticity index (PI) increases exponentially by raising the SAP ratio. The swelling of SAP-soil mixtures increases with SAP ratio. However, applying 20 kPa of normal stress restricts the maximum axial strain to 2.17% for SAP-soil mixtures. The swelling of soil+0.5%SAP under 10 kPa of pressure is simulated using GeoStudio, employing the Finite Element Method by integrating SIGMA/W and SEEP/W. This simulation exhibits a significant correlation with the swelling observed during the experimental phase. The wetting-drying cycle tests reveal that, following five cycles, the SAP exhibits insignificant leaching tendencies from the soil. While the maximum absorbency of SAP in a saturated state declines marginally with each repetition of wetting-drying cycles, the reduction remains consistent after the fourth cycle. As a whole, these essays offer a comprehensive analysis of the potential advantages of utilizing SAP as an additive to maintain soil moisture stability, with a specific emphasis on clay soils.

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The full text of this item is not available at this time because the author has placed this item under an embargo until December 20, 2025.

Keywords

Expansive soil, GeoStudio, Shear Strength, Superabsorbent Polymer, Swelling Potential, Wetting-Drying Cycles

Citation

Department

Civil and Environmental Engineering