The soil construction materials cured with biopolymers are gradually being recognized and widely used in engineering areas, such as roadbeds or foundation fills. The strength of biopolymer-solidified soils (BSS) is easily influenced by the change of internal residual moisture content (RMC), however, the quantitative relationship between them remains unclear. Xanthan gum, as a representative of biopolymer, was used in this study to enhance the mechanical properties of silty sand dredged from the Yellow River under different initial water contents and curing temperatures. The unconfined compressive strength (UCS), curing time, water stability and microscopic properties of BSS were investigated via a series of indoor experiments. Results show that the proposed method for quantitatively evaluating the BSS strength using different RMC values was found to be workable compared to that of the traditional cement-treated method under different curing ages. The curing time required for BSS to reach a certain target strength, i.e. 2900 kPa, is reduced to 9.3 h at a higher curing temperature of 90 degrees C. Moreover, BSS exhibits the self-healing properties of strength recovery after re-temperature drying, with a strength recovery ratio above 45%. The control raw soil samples completely disintegrate in water within 10 s, and even lower xanthan gum biopolymer dosages, such as 0.5%, improved stability in water by reducing permeability by sealing the internal voids of the soil. SEM results indicate that the initial water content and curing temperature mainly affect the distribution of effective xanthan gum linkages, and thus significantly improve the strength and water stability of BSS. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Biopolymer-fiber treated soil has great application potential in civil engineering with better mechanical properties and environmental sustainability. However, the durability and strength degradation rules of biopolymerfiber treated soil with different residual moisture content (RMC) values subjected to severe weathering cycles remain unclear. The effects of wetting-drying (W-D) and freezing-thawing (F-T) cycles on xanthan gum biopolymer-jute fiber treated soil (XJTS) with different RMC values are experimentally investigated. Particular emphasis is placed on mechanical strength characteristics, stress-strain behavior, failure patterns, and associated microstructural evolution encompassing pore structure modifications. The results show that when the RMC value of the XJTS material is higher, its mechanical strength is more affected by the F-T cycle. The effect of the W-D cycles on the pore size and distribution in the XJTS material was more significant than F-T cycles, and the percentage of microfissure (>100 mu m) increased from 6.76 % to 50.01 % after the 20th W-D cycle.