In situ synthesis of superabsorbent polymer in soil: A dual-mechanism study on desiccation crack suppression and self-healing behavior

Soil desiccation cracking is ubiquitous in arid and semi-arid environments, and its evolution directly affects foundation stability and ecosystem functions. To improve the operability of superabsorbent polymer (SAP) incorporation and the crack-control performance, this study proposes a “liquid–solid mixing” in situ polymerization strategy, enabling SAP to form a three-dimensional network within the soil matrix, and systematically evaluates the effects of SAP content on water processes and crack evolution. The in situ generated SAP was characterized in terms of structure and morphology using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and ultra-depth-of-field microscopic imaging (EDOF). Combined with laboratory drying tests and quantitative image analysis, the temporal variations in Water content decay, evaporation kinetics, Crack ratio, and crack geometric parameters were tracked. The results indicate that SAP can be successfully polymerized in situ within soil and can significantly slow water loss and suppress crack propagation. At a dosage of 12%, compared with the blank sample (CK), the average Evaporation rate decreased by approximately 20.6% and the total drying time increased by approximately 38.4%; crack development was effectively controlled, with the final Crack ratio approaching 0%. With increasing SAP dosage, Total crack length, Average crack width, and crack morphological complexity all decreased markedly. Under high-dosage conditions, crack openings exhibited a closure tendency during continued drying, suggesting a certain potential for crack self-healing. These findings demonstrate that the proposed in situ polymerization strategy not only expands a convenient route for SAP incorporation into geotechnical media, but also provides a feasible technical pathway and mechanistic basis for the coupled regulation of “water retention–crack suppression” in soils under drying conditions. Preparation of the SAP precursor solution and schematic illustration of the SAP water absorption mechanism, Mechanism of SAP in regulating moisture dynamics and crack evolution during soil drying, Mechanism of soil desiccation cracking and SAP-induced crack suppression/healing • A novel in situ polymerization strategy was proposed for synthesizing superabsorbent polymers (SAPs) directly within the soil matrix using a liquid–solid mixing approach. • The incorporation of SAP significantly delayed soil moisture loss and reduced average evaporation rate, showing a clear dosage-dependent water-retention effect. • SAP-treated soils exhibited substantial reductions in crack ratio, total crack length, average crack width, and fractal dimension, with improved crack suppression and self-healing behavior at higher dosages. • A positive feedback mechanism of “slow release–crack suppression–water retention” was identified, linking moisture regulation with structural stabilization during desiccation. • This work proposes a promising soil enhancement approach for arid regions, offering new perspectives on the interaction mechanisms between SAP and soil and broadening its potential for practical engineering and environmental applications.