Abstract:

Loess is a Quaternary sediment extensively distributed in Northwest China and is commonly used as foundation and construction material in engineering projects. Nevertheless， natural loess is featured by loose porous structure and high water sensitivity， leading to rapid strength degradation， collapse， disintegration， and even landslides upon water immersion， which severely threaten the long-term safety of engineering structures. Traditional loess stabilization methods using cement， lime， and fly ash can effectively enhance soil strength but are associated with high carbon emissions and ecological damage， which are inconsistent with China’s dual carbon policy. In response， environmentally friendly biopolymers and natural fibers have emerged as promising alternatives for sustainable soil improvement. This study aims to investigate the feasibility of using xanthan gum （XG）， an anionic biopolymer， combined with coconut shell fiber （CF） to stabilize loess， focusing on shear strength， disintegration resistance， and synergistic reinforcement mechanisms. A series of consolidated-undrained triaxial shear tests， disintegration tests， and scanning electron microscopy （SEM） tests were conducted on composite-stabilized loess with five XG contents （0%， 0.5%， 1.0%， 1.5%， 2.0%） and five CF contents （0%， 0.25%， 0.50%， 0.75%， 1.00%）. Triaxial test results indicate that XG and CF synergistically enhance the shear strength of loess in a dosage-dependent manner. Specifically， XG exhibits a slightly more pronounced effect on cohesion than on the internal friction angle， while CF demonstrates a substantially stronger effect on the internal friction angle than on cohesion， with an improvement amplitude approximately twice that of cohesion. The optimum dosage combination of 2.0% xanthan gum and 1.00% coconut shell fiber increases the cohesion and internal friction angle by 79% and 73% compared with the unamended loess， respectively. Disintegration tests demonstrate that increasing XG and CF contents gradually reduces the disintegration rate and delays the disintegration process， in which XG plays a dominant role. In particular， when the XG dosage increases from 0% to 0.5%， the disintegration rate of stabilized loess decreases by more than 80% regardless of the CF dosage. The optimum dosage combination of 2.0% XG and 1.00% CF allows the stabilized loess to maintain integrity without obvious disintegration， solving the inherent defect that loess is prone to instability upon water immersion. SEM microstructural observations reveal that XG provides cementation and pore-clogging effects by bonding soil particles， filling pores， and forming water-impermeable gel membranes. CF forms a three-dimensional reinforcing network by embedding in the soil matrix， thus promoting stress transfer and restraining crack propagation. Under the synergistic interaction， XG enhances the interfacial bonding between soil particles and fibers， forming a compact “XG-CF-clay” composite matrix that strengthens interfacial restriction and toughening efficiency. This synergistic effect ultimately improves the shear strength and water stability of loess. The results of this study provide important data and theoretical support for the application and promotion of eco-friendly biopolymer-based soil stabilization technologies in loess areas.

Key words: loess, xanthan gum, coconut shell fiber, triaxial test, disintegration test, SEM