The Influence of Biogels on the Shear Strength of Red Clay

Red clay is prone to stability problems in engineering due to its high porosity ratio, strong hydrophilicity, and high sensitivity of strength to water content. Traditional improvement materials (such as cement and lime) have significant effects but suffer from drawbacks like high energy consumption, high carbon emissions, and environmental damage. To explore a green and sustainable soil improvement method, this study selected three biopolymers—xanthan gum, guar gum, and carrageenan—as modifiers. Through direct shear tests, the effects of these biopolymers on the shear strength characteristics of Guilin red clay were systematically studied. Five dosages (0%, 0.5%, 1%, 1.5%, and 2%) were set, and quick shear tests were conducted under four levels of vertical pressure (100 - 400 kPa) after 7 days of curing to analyze the variation laws of cohesion and internal friction angle. The results show that all three biogels can significantly improve the cohesion of red clay; the optimal dosage of xanthan gum and guar gum is 1.5%, at which the shear strength is the highest; carrageenan achieves the best improvement effect at a dosage of 1%. Cohesion first increases and then decreases with the increase of dosage, while the variation law of internal friction angle varies with the type of biogel (xanthan gum shows an opposite change, guar gum first increases and then decreases, and carrageenan first decreases and then increases), and the overall variation range is smaller than that of cohesion. This study provides a theoretical basis and technical reference for the green improvement of red clay.